Updated on 2021/10/29

写真a

 
SHIOKAWA, Kazuo
 
Organization
Institute for Space-Earth Environmental Research Center for International Collaborative Research Professor
Graduate School
Graduate School of Engineering
Title
Professor
External link

Degree 2

  1. Doctor of Science ( 1994.7   Nagoya University ) 

  2. 理学修士 ( 1990.3   東北大学 ) 

Research Interests 5

  1. ionosphere

  2. magnetosphere

  3. airglow

  4. aeronomy

  5. aurora

Research Areas 2

  1. Others / Others  / Aeronomy and Magnetospheric Physics

  2. Natural Science / Space and planetary sciences

Current Research Project and SDGs 4

  1. Study on the atmospheric dynamics in the mesosphere and thermosphere

  2. Plasma and electromagnetic field variations in the inner magnetosphere

  3. Magnetospheric plasma physics related to substorm

  4. Study on the production mechanisms of low-latitude auroras observed in Japan

Research History 1

  1. Nagoya University   Institute for Space-Earth Environmental Research Center for International Collaborative Research   Professor

    2015.10

Awards 2

  1. 2010 Editors' Citation for Excellence in Refereeing for JGR-Space Physics

    2011  

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    Country:United States

  2. Tanakadate Award

    2009.5   Society of Geomagnetism and Earth, Planetary and Space Sciences  

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    Country:Japan

 

Papers 561

  1. PSTEP: project for solar–terrestrial environment prediction Reviewed

    Kusano K., Ichimoto K., Ishii M., Miyoshi Y., Yoden S., Akiyoshi H., Asai A., Ebihara Y., Fujiwara H., Goto T.N., Hanaoka Y., Hayakawa H., Hosokawa K., Hotta H., Hozumi K., Imada S., Iwai K., Iyemori T., Jin H., Kataoka R., Katoh Y., Kikuchi T., Kubo Y., Kurita S., Matsumoto H., Mitani T., Miyahara H., Miyoshi Y., Nagatsuma T., Nakamizo A., Nakamura S., Nakata H., Nishizuka N., Otsuka Y., Saito S., Saito S., Sakurai T., Sato T., Shimizu T., Shinagawa H., Shiokawa K., Shiota D., Takashima T., Tao C., Toriumi S., Ueno S., Watanabe K., Watari S., Yashiro S., Yoshida K., Yoshikawa A.

    Earth, Planets and Space   Vol. 73 ( 1 )   2021.12

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Earth, Planets and Space  

    Although solar activity may significantly impact the global environment and socioeconomic systems, the mechanisms for solar eruptions and the subsequent processes have not yet been fully understood. Thus, modern society supported by advanced information systems is at risk from severe space weather disturbances. Project for solar–terrestrial environment prediction (PSTEP) was launched to improve this situation through synergy between basic science research and operational forecast. The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. By this project, we sought to answer the fundamental questions concerning the solar–terrestrial environment and aimed to build a next-generation space weather forecast system to prepare for severe space weather disasters. The PSTEP consists of four research groups and proposal-based research units. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.[Figure not available: see fulltext.]

    DOI: 10.1186/s40623-021-01486-1

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  2. Isolated Proton Aurora Driven by EMIC Pc1 Wave: PWING, Swarm, and NOAA POES Multi-Instrument Observations Reviewed

    Kim H., Shiokawa K., Park J., Miyoshi Y., Miyashita Y., Stolle C., Connor H.K., Hwang J., Buchert S., Kwon H.J., Nakamura S., Nakamura K., Oyama S.I., Otsuka Y., Nagatsuma T., Sakaguchi K.

    Geophysical Research Letters   Vol. 48 ( 18 )   2021.9

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Geophysical Research Letters  

    We report the concurrent observations of F-region plasma changes and field-aligned currents (FACs) above isolated proton auroras (IPAs) associated with electromagnetic ion cyclotron Pc1 waves. Key events on March 19, 2020 and September 12, 2018 show that ground magnetometers and all-sky imagers detected concurrent Pc1 wave and IPA, during which NOAA POES observed precipitating energetic protons. In the ionospheric F-layer above the IPA zone, the Swarm satellites observed transverse Pc1 waves, which span wider latitudes than IPA. Around IPA, Swarm also detected the bipolar FAC and localized plasma density enhancement, which is occasionally surrounded by wide/shallow depletion. This indicates that wave-induced proton precipitation contributes to the energy transfer from the magnetosphere to the ionosphere.

    DOI: 10.1029/2021GL095090

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  3. An experimental investigation into the possible connections between the zonal neutral wind speeds and equatorial plasma bubble drift velocities over the African equatorial region Reviewed

    Okoh D.I., Rabiu A.B., Shiokawa K., Otsuka Y., Wu Q., Seemala G.K., Katamzi-Joseph Z.T.

    Journal of Atmospheric and Solar-Terrestrial Physics   Vol. 220   2021.9

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Journal of Atmospheric and Solar-Terrestrial Physics  

    There is increasing interest to understand thermospheric neutral wind and ionized plasma coupling, especially by using empirical observations. This is the first study that reports simultaneous measurements of thermospheric neutral wind and equatorial plasma bubble (EPB) speeds over the African equatorial region. Neutral wind speeds were obtained using a Fabry-Perot interferometer (FPI), while EPB speeds were obtained using an all-sky optical imager. Both instruments are co-located in Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S). Data for 11 nights of coincident neutral wind and EPB speed observations were used. The neutral wind speeds were in the range of about −30 to 300 m/s, while EPB speeds were in the range of about 15–400 m/s. The speeds of both neutral winds and EPBs were generally observed to be faster during the early night hours and to slow down towards midnight. In some instances, the neutral wind and EPB speeds were comparable, an observation that is in agreement with full development of the F region dynamo. There were also instances in which the EPBs were faster or slower than the neutral winds. In one of the nights, a southward turning of the IMF-Bz was observed to cause a sudden increase in the EPB speed. For some nights, the neutral winds were faster than the EPBs during earlier hours of the nights, and the disparity reduced during the later hours of the nights. This was attributed to the possibility that the F region dynamo was yet to be fully developed during the earlier hours.

    DOI: 10.1016/j.jastp.2021.105663

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  4. First Simultaneous Observation of a Night Time Medium‐Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite Reviewed

    K. Kawai, K. Shiokawa, Y. Otsuka, S. Oyama, Y. Kasaba, Y. Kasahara, F. Tsuchiya, A. Kumamoto, S. Nakamura, A. Matsuoka, S. Imajo, Y. Kazama, S.‐Y. Wang, S. W. Y. Tam, T. F. Chang, B. J. Wang, K. Asamura, S. Kasahara, S. Yokota, K. Keika, T. Hori, Y. Miyoshi, C. Jun, M. Shoji, I. Shinohara

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 9 )   2021.9

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union (AGU)  

    DOI: 10.1029/2020ja029086

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029086

  5. Multi-instrument study of longitudinal wave structures for plasma bubble seeding in the equatorial ionosphere Reviewed

    Takahashi H., Essien P., Figueiredo C. A. O. B., Wrasse C. M., Barros D., Abdu M. A., Otsuka Y., Shiokawa K., Li GuoZhu

    EARTH AND PLANETARY PHYSICS   Vol. 5 ( 5 ) page: 368 - 377   2021.9

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Earth and Planetary Physics  

    Large Scale Wave Structures (LSWS) in the equatorial ionospheric F-region were observed by measuring spatial and temporal variations within detrended total electron content (dTEC) data obtained by ground-based GNSS receivers over the South American continent. By using dTEC-maps, we have been able to produce, for the first-time, two-dimensional representations of LSWS. During the period from September to December, the LSWS frequently occurred starting a few hours prior to Equatorial Plasma Bubble (EPB) development. From 17 events of LSWS observed in 2014 and 2015, wave characteristics were obtained: the observed wavelengths, periods, and the phase speeds are respectively, ~900 km, ~41 min and ~399 m/s; the waves propagated from the northeast to southeast. In some cases the front of the oscillation was meridionally aligned, extending to more than 1600 km, the first time such large extension of the wavefront has been reported. From F-layer bottom height oscillation data, measured by ionosonde, LSWS exhibit two different vertical phase propagation modes, in-phase and downward phase. The former mode indicates the presence of a polarization electric field in the F-layer bottom side; the latter suggests propagation of atmospheric gravity waves. The presence of LSWS near the solar terminator, followed by the development of EPBs, suggests that the upwelling of the F-layer bottom height produces a condition favorable to the development of Rayleigh–Taylor instability.

    DOI: 10.26464/epp2021047

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  6. Spatial Evolution of Wave‐Particle Interaction Region Deduced From Flash‐Type Auroras and Chorus‐Ray Tracing Reviewed

    Mitsunori Ozaki, Tomohiro Inoue, Yoshimasa Tanaka, Satoshi Yagitani, Yoshiya Kasahara, Kazuo Shiokawa, Yoshizumi Miyoshi, Kousuke Imamura, Keisuke Hosokawa, Shin‐ichiro Oyama, Ryuho Kataoka, Yusuke Ebihara, Yasunobu Ogawa, Akira Kadokura

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 7 )   2021.7

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union (AGU)  

    DOI: 10.1029/2021JA029254

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JA029254

  7. What controls the luminosity of polar cap airglow patches?: Implication from airglow measurements in Eureka, Canada in comparison with SuperDARN convection pattern Reviewed

    Hosokawa K., Nagata M., Shiokawa K., Otsuka Y.

    POLAR SCIENCE   Vol. 28   2021.6

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Polar Science  

    Polar cap patches are known as islands of enhanced electron density in the polar cap F region ionosphere. To observe the airglow signature of polar cap patches continuously at a fixed point near the center of the MLAT/MLT coordinate system, we started operating an all-sky imager in Eureka, Canada since 2015, where the magnetic latitude is ~87°. By statistically analyzing the 630-nm airglow images from Eureka, it was identified that the luminosity of patches, which is proportional to the electron density in the F region, increases during specific UT interval from 16 to 22 UT. This outstanding UT variation of patch luminosity can be explained simply by the systematic shift of the terminator in the MLAT/MLT coordinate system due to the offset between the geographic and geomagnetic pole. That is, the spatial relationship between the dense source plasma in the sunlit area and the high-latitude convection system controls the UT variation. We also found that when the IMF By is positive, the number of polar cap patches was twice of that in the negative IMF By. By deriving average convection patterns from the archived SuperDARN map potential data, we confirmed that the configuration of plasma convection is more appropriate for patches to be transported toward the magnetic pole during the positive IMF By condition.

    DOI: 10.1016/j.polar.2020.100608

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  8. Influence of Zonal Wind Velocity Variation on Equatorial Plasma Bubble Occurrences Over Southeast Asia Reviewed

    Sarudin I., Hamid N.S.A., Abdullah M., Buhari S.M., Shiokawa K., Otsuka Y., Hozumi K., Jamjareegulgarn P.

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 5 )   2021.5

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research: Space Physics  

    The present study aims to investigate the influence of the zonal wind velocity on equatorial plasma bubble (EPB) occurrences over Southeast Asia. The observation of the EPB occurrence is obtained from the GPS Rate of TEC change index. Meanwhile, the zonal winds were measured using a Fabry-Perot interferometer located at Kototabang and Chiang Mai stations, and the height of F layer was acquired using an ionosonde at Chumphon station near the magnetic equator. This is the first study to report the influence of zonal wind velocity variation on EPB occurrences with the presence and absence of EPB using GPS data in the Southeast Asian sector. The results illustrated that the average magnitude of zonal wind velocity during the presence of EPB (78 ± 23 m/s) was higher than that of its absence (68 ± 21 m/s). It was observed using long-term data analyses which led to in-depth analyses. The analysis of temporal variation of zonal wind variation demonstrated that the zonal winds during EPB were higher in the evening compared to midnight and postmidnight periods from medium to high solar activities. The dependence of zonal wind velocity on EPB over local time was obtained based on the analysis which utilized the data collected during equinox in high solar activity. Besides that, a positive correlation was obtained between the zonal wind velocity and EPB occurrences during pre-reversal enhancement (PRE) corroborated the effects of zonal wind influence on PRE, and thus EPB occurrences.

    DOI: 10.1029/2020JA028994

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  9. Simultaneous Observation of Two Isolated Proton Auroras at Subauroral Latitudes by a Highly Sensitive All-Sky Camera and Van Allen Probes Reviewed

    Nakamura K., Shiokawa K., Otsuka Y., Shinbori A., Miyoshi Y., Connors M., Spence H., Reeves G., Funsten H.O., MacDowall R., Smith C., Wygant J., Bonnell J.

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 5 )   2021.5

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research: Space Physics  

    Isolated proton auroras (IPAs) appearing at subauroral latitudes are generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. An IPA thus indicates the spatial scale and temporal variation of wave-particle interactions in the magnetosphere. In this study, a unique event of simultaneous ground and magnetospheric satellite observations of two IPAs were conducted on March 16, 2015, using an all-sky imager at Athabasca, Canada and Van Allen Probes. The Van Allen Probes observed two isolated EMIC waves with frequencies of ∼1 and 0.4 Hz at L ≈ 5.0 when the satellite footprint crossed over the two IPAs. This suggests that the IPAs were caused by localized EMIC waves. Proton flux at 5–20 keV increased locally when the EMIC waves appeared. Electron flux at energies below ∼500 eV also increased. Temperature anisotropy of the energetic protons was estimated at 1.5–2.5 over a wide L-value range of 3.0–5.2. Electron density gradually decreased from L = 3.5 to 5.4, suggesting that the EMIC wave at L ≈ 5.0 was located in the gradual plasmapause. From these observations, we conclude that the localized IPAs and associated EMIC waves took place because of localized enhancement of energetic proton flux and plasma density structure near the plasmapause. The magnetic field observed by the satellite showed small variation during the wave observation, indicating that the IPAs were accompanied by the weak field-aligned current.

    DOI: 10.1029/2020JA029078

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  10. Multi‐Event Analysis of Plasma and Field Variations in Source of Stable Auroral Red (SAR) Arcs in Inner Magnetosphere During Non‐Storm‐Time Substorms Reviewed

    Yudai Inaba, Kazuo Shiokawa, Shin‐ichiro Oyama, Yuichi Otsuka, Martin Connors, Ian Schofield, Yoshizumi Miyoshi, Shun Imajo, Atsuki Shinbori, Artem Yu Gololobov, Yoichi Kazama, Shiang‐Yu Wang, Sunny W. Y. Tam, Tzu‐Fang Chang, Bo‐Jhou Wang, Kazushi Asamura, Shoichiro Yokota, Satoshi Kasahara, Kunihiro Keika, Tomoaki Hori, Ayako Matsuoka, Yoshiya Kasahara, Atsushi Kumamoto, Shoya Matsuda, Yasumasa Kasaba, Fuminori Tsuchiya, Masafumi Shoji, Masahiro Kitahara, Satoko Nakamura, Iku Shinohara, Harlan E. Spence, Geoff D. Reeves, Robert J. Macdowall, Charles W. Smith, John R. Wygant, John W. Bonnell

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 4 )   2021.4

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union (AGU)  

    DOI: 10.1029/2020ja029081

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029081

  11. Preface of the special issue: "Variability of the Sun and Its Terrestrial Impact (VarSITI) Completion Symposium 2019 and the SCOSTEP 14th Quadrennial Solar-Terrestrial Physics Symposium (STP14)" Preface Reviewed

    Shiokawa Kazuo, Dasso Sergio, Miteva Rositsa, Pallamraju Duggirala, Zhang Shun-Rong

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 215   2021.4

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Journal of Atmospheric and Solar-Terrestrial Physics  

    DOI: 10.1016/j.jastp.2021.105593

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  12. Magnetic Conjugacy of Pc1 Waves and Isolated Proton Precipitation at Subauroral Latitudes: Importance of Ionosphere as Intensity Modulation Region Reviewed

    Mitsunori Ozaki, Kazuo Shiokawa, Richard B. Horne, Mark J. Engebretson, Marc Lessard, Yasunobu Ogawa, Keisuke Hosokawa, Masahito Nosé, Yusuke Ebihara, Akira Kadokura, Satoshi Yagitani, Yoshizumi Miyoshi, Shion Hashimoto, Shipra Sinha, Ashwini K. Sinha, Gopi K. Seemala, Chae‐Woo Jun

    Geophysical Research Letters   Vol. 48 ( 5 )   2021.3

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union (AGU)  

    DOI: 10.1029/2020gl091384

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GL091384

  13. A review of the SCOSTEP's 5-year scientific program VarSITI-Variability of the Sun and Its Terrestrial Impact Reviewed

    Shiokawa Kazuo, Georgieva Katya

    PROGRESS IN EARTH AND PLANETARY SCIENCE   Vol. 8 ( 1 )   2021.3

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Progress in Earth and Planetary Science  

    The Sun is a variable active-dynamo star, emitting radiation in all wavelengths and solar-wind plasma to the interplanetary space. The Earth is immersed in this radiation and solar wind, showing various responses in geospace and atmosphere. This Sun–Earth connection variates in time scales from milli-seconds to millennia and beyond. The solar activity, which has a ~11-year periodicity, is gradually declining in recent three solar cycles, suggesting a possibility of a grand minimum in near future. VarSITI—variability of the Sun and its terrestrial impact—was the 5-year program of the scientific committee on solar-terrestrial physics (SCOSTEP) in 2014–2018, focusing on this variability of the Sun and its consequences on the Earth. This paper reviews some background of SCOSTEP and its past programs, achievements of the 5-year VarSITI program, and remaining outstanding questions after VarSITI. [Figure not available: see fulltext.]

    DOI: 10.1186/s40645-021-00410-1

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  14. GPS Scintillations and TEC Variations in Association With a Polar Cap Arc Reviewed

    Wang Y., Cao Z., Xing Z.Y., Zhang Q.H., Jayachandran P.T., Oksavik K., Balan N., Shiokawa K.

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 3 )   2021.3

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research: Space Physics  

    A unique example of a polar cap arc producing clear amplitude and phase scintillations in GPS L-band signals is presented using observations from an all-sky imager and a GPS receiver and a digital ionosonde at Resolute Bay and the SuperDARN Inuvik radar. During the southward interplanetary magnetic field (IMF) condition, the polar cap arc moved quickly from the dusk-side to the midnight auroral oval at a speed of ∼700 m/s, as revealed by all-sky 557.7 and 630.0 nm images. When it intersected the raypath of GPS signals, both amplitude and phase scintillations appeared, which is very different from previous results. Moreover, the scintillations were precisely determined through power spectral analysis. We propose that the strong total electron content (TEC) enhancement (∼6 TECU) and flow shears in association with the polar cap arc under the southward IMF condition were creating the scintillations. It provides evidence for the existence of polar cap arc scintillations that may be harmful for satellite applications even through L-band signals.

    DOI: 10.1029/2020JA028968

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  15. Statistical Analysis of Pc1 Wave Ducting Deduced From Swarm Satellites Reviewed

    Kim H., Shiokawa K., Park J., Miyoshi Y., Stolle C., Buchert S.

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 3 )   2021.3

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research: Space Physics  

    Transverse Pc1 waves propagating from magnetospheric source regions undergo mode conversion to the compressional mode in the ionosphere due to the induced Hall current. Mode converted Pc1 waves propagate across the magnetic field through the ionospheric waveguide. This process is called Pc1 wave ducting (PWD). PWDs have been observed by magnetometers on both ground and low Earth orbit satellites over a wide latitudinal and longitudinal range. In this work, we present the statistical analysis results of PWD exploiting Swarm satellites from 2015 to 2019. Spatial distributions show that the PWDs are mainly observed over the South Atlantic Anomaly longitudes, possibly due to the high Hall conductivity and F-region density, and at subauroral/auroral latitudes ((Formula presented.) MLAT). The occurrence rate of PWD increases with increasing AE and (Formula presented.) SYM-H (Formula presented.) indices. Seasonal dependence shows that PWD exhibits a high occurrence rate during equinox and local summer while local winter hosts only a low occurrence. The asymmetry between summer and winter can be explained by the ionospheric plasma density. The high occurrence rate in equinox may result from intense geomagnetic activity during the equinox, probably due to the Russell-McPherron effect. From our statistical analysis, we conclude that the occurrence of PWD is controlled by both ionospheric plasma conditions and geomagnetic activity, and that the mode conversion and PWD occur more efficiently as plasma density increases.

    DOI: 10.1029/2020JA029016

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  16. Investigation of Small‐Scale Electron Density Irregularities Observed by the Arase and Van Allen Probes Satellites Inside and Outside the Plasmasphere Reviewed

    Neethal Thomas, Kazuo Shiokawa, Yoshizumi Miyoshi, Yoshiya Kasahara, Iku Shinohara, Atsushi Kumamoto, Fuminori Tsuchiya, Ayako Matsuoka, Satoshi Kasahara, Shoichiro Yokota, Kunihiro Keika, Tomoaki Hori, Kazushi Asamura, Shiang‐Yu Wang, Yoichi Kazama, Sunny Wing‐Yee Tam, Tzu‐Fang Chang, Bo‐Jhou Wang, John Wygant, Aaron Breneman, Geoffrey Reeves

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 3 )   2021.3

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union (AGU)  

    DOI: 10.1029/2020ja027917

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA027917

  17. Formation of an additional density peak in the bottom side of the sodium layer associated with the passage of multiple mesospheric frontal systems Reviewed

    Viswanathan Lakshmi Narayanan, Satonori Nozawa, Shin-Ichiro Oyama, Ingrid Mann, Kazuo Shiokawa, Yuichi Otsuka, Norihito Saito, Satoshi Wada, Takuya D. Kawahara, Toru Takahashi

    ATMOSPHERIC CHEMISTRY AND PHYSICS   Vol. 21 ( 4 ) page: 2343 - 2361   2021.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:COPERNICUS GESELLSCHAFT MBH  

    We present a detailed investigation of the formation of an additional sodium density peak at altitudes of 79-85 km below the main peak of the sodium layer based on sodium lidar and airglow imager measurements made at Ramfjordmoen near Tromso, Norway, on the night of 19 December 2014. The airglow imager observations of OH emissions revealed four passing frontal systems that resembled mesospheric bores, which typically occur in ducting regions of the upper mesosphere. For about 1.5 h, the lower-altitude sodium peak had densities similar to that of the main peak of the layer around 90 km. The lower-altitude sodium peak weakened and disappeared soon after the fourth front had passed. The fourth front had weakened in intensity by the time it approached the region of lidar beams and disappeared soon afterwards. The column-integrated sodium densities increased gradually during the formation of the lower-altitude sodium peak. Temperatures measured with the lidar indicate that there was a strong thermal duct structure between 87 and 93 km. Furthermore, the temperature was enhanced below 85 km. Horizontal wind magnitudes estimated from the lidar showed strong wind shears above 93 km. We conclude that the combination of an enhanced stability region due to the temperature profile and intense wind shears have provided ideal conditions for evolution of multiple mesospheric bores revealed as frontal systems in the OH images. The downward motion associated with the fronts appeared to have brought air rich in H and O from higher altitudes into the region below 85 km, wherein the temperature was also higher. Both factors would have liberated sodium atoms from the reservoir species and suppressed the reconversion of atomic sodium into reservoir species so that the lower-altitude sodium peak could form and the column abundance could increase. The presented observations also reveal the importance of mesospheric frontal systems in bringing about significant variation of minor species over shorter temporal intervals.

    DOI: 10.5194/acp-21-2343-2021

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  18. Study of Spatiotemporal Development of Global Distribution of Magnetospheric ELF/VLF Waves Using Ground-Based and Satellite Observations, and RAM-SCB Simulations, for the March and November 2017 Storms Reviewed

    Takeshita Y., Shiokawa K., Miyoshi Y., Ozaki M., Kasahara Y., Oyama S.i., Connors M., Manninen J., Jordanova V.K., Baishev D., Oinats A., Kurkin V.

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 2 )   2021.2

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research: Space Physics  

    Magnetospheric Extremely Low-Frequency/Very Low-Frequency (ELF/VLF) waves have an important role in the acceleration and loss of energetic electrons in the magnetosphere through wave-particle interaction. It is necessary to understand the spatiotemporal development of magnetospheric ELF/VLF waves to quantitatively estimate this effect of wave-particle interaction, a global process not yet well understood. We investigated spatiotemporal development of magnetospheric ELF/VLF waves using 6 PWING ground-based stations at subauroral latitudes, Exploration of energization and Radiation in Geospace and RBSP satellites, POES/MetOp satellites, and the RAM-SCB model, focusing on the March and November 2017 storms driven by corotating interaction regions in the solar wind. Our results show that the ELF/VLF waves are enhanced over a longitudinal extent from midnight to morning and dayside associated with substorm electron injections. In the main to early storm recovery phase, we observe continuous ELF/VLF waves from ∼0 to ∼12 MLT in the dawn sector. This wide extent seems to be caused by frequent occurrence of substorms. The wave region expands eastward in association with the drift of source electrons injected by substorms from the nightside. We also observed dayside ELF/VLF wave enhancement, possibly driven by magnetospheric compression by solar wind, over an MLT extent of at least 5 h. Ground observations tend not to observe ELF/VLF waves in the post-midnight sector, although other methods clearly show the existence of waves. This is possibly due to Landau damping of the waves, the absence of the plasma density duct structure, and/or enhanced auroral ionization of the ionosphere in the post-midnight sector.

    DOI: 10.1029/2020JA028216

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  19. Multievent Study of Characteristics and Propagation of Naturally Occurring ELF/VLF Waves Using High‐Latitude Ground Observations and Conjunctions With the Arase Satellite Reviewed

    C. Martinez‐Calderon, Y. Katoh, J. Manninen, O. Santolik, Y. Kasahara, S. Matsuda, A. Kumamoto, F. Tsuchiya, A. Matsuoka, M. Shoji, M. Teramoto, I. Shinohara, K. Shiokawa, Y. Miyoshi

    Journal of Geophysical Research: Space Physics   Vol. 126 ( 2 )   2021.2

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:American Geophysical Union (AGU)  

    DOI: 10.1029/2020ja028682

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA028682

  20. Multi-Wavelength Imaging Observations of STEVE at Athabasca, Canada Reviewed

    Yadav Sneha, Shiokawa Kazuo, Otsuka Yuichi, Connors Martin, St Maurice J-P

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 126 ( 2 )   2021.2

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research: Space Physics  

    We present the first multi-wavelength imaging observations of strong thermal emission velocity enhancement (STEVE) using an all-sky imager at Athabasca (magnetic latitude = 61.5°N), Canada. This study is based on three STEVE events which were accompanied by picket fence structures in the green-line. Although the STEVE arc was dominant in 630 and 557.7-nm, weak emissions were also found in other wavelengths including OI at 844.6, Hβ, Na, and the nominal background filter at 572.5-nm. As observed at 630 and 557.7-nm, the STEVE arc started as a faint arc close to the auroral oval and moved equatorward. The 557.7-nm arc exhibited picket fence structure at later times after it moved equatorward. The picket fence was sometimes found to persist even after the 630-nm arc had disappeared. During a particular event, the STEVE arcs in both the 630 and 557.7-nm were found to carry a ribbon-like motion moving along the arc. We have found that STEVE arcs are embedded in a region of weak diffuse auroral emissions. The STEVE arcs have sharp boundaries and these boundaries are different in red- and green-line. The sharp decrease in the intensity at the immediate poleward edge of the STEVE arc appears as a “dark-band” in the green-line images. Based on the horizontal component of the geomagnetic field at Fort Smith (magnetic latitude 67.28°N), we find that the STEVE arc detachment, its equatorward motion, and its brightness coincided with changes in the magnetic activity during the recovery phase of a substorm.

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  21. Active auroral arc powered by accelerated electrons from very high altitudes Reviewed

    Shun Imajo, Yoshizumi Miyoshi, Yoichi Kazama, Kazushi Asamura, Iku Shinohara, Kazuo Shiokawa, Yoshiya Kasahara, Yasumasa Kasaba, Ayako Matsuoka, Shiang-Yu Wang, Sunny W. Y. Tam, Tzu-Fang Chang, Bo-Jhou Wang, Vassilis Angelopoulos, Chae-Woo Jun, Masafumi Shoji, Satoko Nakamura, Masahiro Kitahara, Mariko Teramoto, Satoshi Kurita, Tomoaki Hori

    SCIENTIFIC REPORTS   Vol. 11 ( 1 ) page: 1610   2021.1

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    Bright, discrete, thin auroral arcs are a typical form of auroras in nightside polar regions. Their light is produced by magnetospheric electrons, accelerated downward to obtain energies of several kilo electron volts by a quasi-static electric field. These electrons collide with and excite thermosphere atoms to higher energy states at altitude of similar to 100 km; relaxation from these states produces the auroral light. The electric potential accelerating the aurora-producing electrons has been reported to lie immediately above the ionosphere, at a few altitudes of thousand kilometres(1). However, the highest altitude at which the precipitating electron is accelerated by the parallel potential drop is still unclear. Here, we show that active auroral arcs are powered by electrons accelerated at altitudes reaching greater than 30,000 km. We employ high-angular resolution electron observations achieved by the Arase satellite in the magnetosphere and optical observations of the aurora from a ground-based all-sky imager. Our observations of electron properties and dynamics resemble those of electron potential acceleration reported from low-altitude satellites except that the acceleration region is much higher than previously assumed. This shows that the dominant auroral acceleration region can extend far above a few thousand kilometres, well within the magnetospheric plasma proper, suggesting formation of the acceleration region by some unknown magnetospheric mechanisms.

    DOI: 10.1038/s41598-020-79665-5

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  22. Development of research capacities in space weather: A successful international cooperation Reviewed

    Amory-Mazaudier C., Radicella S., Doherty P., Gadimova S., Fleury R., Nava B., Anas E., Petitdidier M., Migoya-Orué Y., Alazo-Cuartas K., Shiokawa K.

    Journal of Space Weather and Space Climate   Vol. 11   2021

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    This paper presents an international cooperation which has successfully developed research capacities in the scientific disciplines of sun-earth relations and space weather in many countries over the world during the past decades. This success was based on the deployment of scientific instruments in countries that did not have them, on the sharing of knowledge and research tools, on thesis supervision and on the integration of researchers trained in their country. This article will only focus on aspects of training conducted by ICTP, Boston College, ICG, SCOSTEP and GIRGEA. We will highlight what has been enhanced in international cooperation to achieve this success and what remains to be done.

    DOI: 10.1051/swsc/2021006

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  23. Oxygen torus and its coincidence with EMIC wave in the deep inner magnetosphere: Van Allen Probe B and Arase observations Reviewed

    M. Nosé, A. Matsuoka, A. Kumamoto, Y. Kasahara, M. Teramoto, S. Kurita, J. Goldstein, L. M. Kistler, S. Singh, A. Gololobov, K. Shiokawa, S. Imajo, S. Oimatsu, K. Yamamoto, Y. Obana, M. Shoji, F. Tsuchiya, I. Shinohara, Y. Miyoshi, W. S. Kurth, C. A. Kletzing, C. W. Smith, R. J. MacDowall, H. Spence, G. D. Reeves

    Earth, Planets and Space   Vol. 72 ( 1 )   2020.12

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    <title>Abstract</title>
    We investigate the longitudinal structure of the oxygen torus in the inner magnetosphere for a specific event found on 12 September 2017, using simultaneous observations from the Van Allen Probe B and Arase satellites. It is found that Probe B observed a clear enhancement in the average plasma mass (<italic>M</italic>) up to 3–4 amu at <italic>L</italic> = 3.3–3.6 and magnetic local time (MLT) = 9.0 h. In the afternoon sector at MLT ~ 16.0 h, both Probe B and Arase found no clear enhancements in <italic>M</italic>. This result suggests that the oxygen torus does not extend over all MLT but is skewed toward the dawn. Since a similar result has been reported for another event of the oxygen torus in a previous study, a crescent-shaped torus or a pinched torus centered around dawn may be a general feature of the O<sup>+</sup> density enhancement in the inner magnetosphere. We newly find that an electromagnetic ion cyclotron (EMIC) wave in the H<sup>+</sup> band appeared coincidently with the oxygen torus. From the lower cutoff frequency of the EMIC wave, the ion composition of the oxygen torus is estimated to be 80.6% H<sup>+</sup>, 3.4% He<sup>+</sup>, and 16.0% O<sup>+</sup>. According to the linearized dispersion relation for EMIC waves, both He<sup>+</sup> and O<sup>+</sup> ions inhibit EMIC wave growth and the stabilizing effect is stronger for He<sup>+</sup> than O<sup>+</sup>. Therefore, when the H<sup>+</sup> fraction or <italic>M</italic> is constant, the denser O<sup>+</sup> ions are naturally accompanied by the more tenuous He<sup>+</sup> ions, resulting in a weaker stabilizing effect (i.e., larger growth rate). From the Probe B observations, we find that the growth rate becomes larger in the oxygen torus than in the adjacent regions in the plasma trough and the plasmasphere.

    DOI: 10.1186/s40623-020-01235-w

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    Other Link: http://link.springer.com/article/10.1186/s40623-020-01235-w/fulltext.html

  24. An Ephemeral Red Arc Appeared at 68° MLat at a Pseudo Breakup During Geomagnetically Quiet Conditions Reviewed

    S. Oyama, A. Shinbori, Y. Ogawa, M. Kellinsalmi, T. Raita, A. Aikio, H. Vanhamäki, K. Shiokawa, I. Virtanen, L. Cai, A. B. Workayehu, M. Pedersen, K. Kauristie, T. T. Tsuda, B. Kozelov, A. Demekhov, A. Yahnin, F. Tsuchiya, A. Kumamoto, Y. Kasahara, A. Matsuoka, M. Shoji, M. Teramoto, M. Lester

    Journal of Geophysical Research: Space Physics   Vol. 125 ( 10 )   2020.10

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    DOI: 10.1029/2020ja028468

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  25. Plasma and Field Observations in the Magnetospheric Source Region of a Stable Auroral Red (SAR) Arc by the Arase Satellite on 28 March 2017 Reviewed

    Yudai Inaba, Kazuo Shiokawa, Shin-ichiro Oyama, Yuichi Otsuka, Arto Oksanen, Atsuki Shinbori, Artem Yu Gololobov, Yoshizumi Miyoshi, Yoichi Kazama, Shiang-Yu Wang, Sunny W. Y. Tam, Tzu-Fang Chang, Bo-Jhou Wang, Shoichiro Yokota, Satoshi Kasahara, Kunihiro Keika, Tomoaki Hori, Ayako Matsuoka, Yoshiya Kasahara, Atsushi Kumamoto, Yasumasa Kasaba, Fuminori Tsuchiya, Masafumi Shoji, Iku Shinohara, Claudia Stolle

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 10 )   2020.10

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    A stable auroral red (SAR) arc is an aurora with a dominant 630 nm emission at subauroral latitudes. SAR arcs have been considered to occur due to the spatial overlap between the plasmasphere and the ring-current ions. In the overlap region, plasmaspheric electrons are heated by ring-current ions or plasma waves, and their energy is then transferred down to the ionosphere where it causes oxygen red emission. However, there have been no study conducted so far that quantitatively examined plasma and electromagnetic fields in the magnetosphere associated with SAR arc. In this paper, we report the first quantitative evaluation of conjugate measurements of a SAR arc observed at 2204 UT on 28 March 2017 and investigate its source region using an all-sky imager at Nyrola (magnetic latitude: 59.4 degrees N), Finland, and the Arase satellite. The Arase observation shows that the SAR arc appeared in the overlap region between a plasmaspheric plume and the ring-current ions and that electromagnetic ion cyclotron waves and kinetic Alfven waves were not observed above the SAR arc. The SAR arc was located at the ionospheric trough minimum identified from a total electron content map obtained by the GNSS receiver network. The Swarm satellite flying in the ionosphere also passed the SAR arc at similar to 2320 UT and observed a decrease in electron density and an increase in electron temperature during the SAR-arc crossing. These observations suggest that the heating of plasmaspheric electrons via Coulomb collision with ring-current ions is the most plausible mechanism for the SAR-arc generation.Plain Language Summary A stable auroral red (SAR) arc is an aurora with an optical red emission at latitudes slightly lower than the auroral zone. SAR arcs have been considered to occur due to the spatial overlap between the low-energy plasmaspheric electrons and the high-energy ring-current ions. In the overlap region, plasmaspheric electrons are heated by ring-current ions or plasma waves, and their energy is then transferred down to the upper atmosphere to cause the red emission. However, there have been no study conducted so far that quantitatively examined plasma and electromagnetic fields in the magnetospheric source region of SAR arcs. In this paper, we report the first quantitative evaluation of a SAR arc using an all-sky imager at Nyrola, Finland, and the Arase satellite. The Arase observation shows that the SAR arc appeared in the overlap region between a plasmaspheric plume and the ring-current ions in the inner magnetosphere. The electromagnetic waves associated with the SAR arc were not observed. These observations suggest that the heating of plasmaspheric electrons by ring-current ions is the most plausible mechanism for the SAR-arc generation. This result provides direct evidence of the previous theoretical expectation on the generation mechanism of red aurora at lower latitudes.

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  26. Equatorial Plasma Bubble Occurrence Under Propagation of MSTID and MLT Gravity Waves Reviewed

    Takahashi H., Wrasse C. M., Figueiredo C. A. O. B., Barros D., Paulino I., Essien P., Abdu M. A., Otsuka Y., Shiokawa K.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 9 )   2020.9

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    We observed a signature of equatorial plasma bubbles (EPBs) followed by a medium-scale traveling ionospheric disturbance (MSTID) crossing the solar terminator over the geomagnetic equator during the period of post-sunset rise (PSSR) of the F layer. Simultaneous observations of the EPBs and the MSTIDs by ground-based Global Navigation Satellite System receivers and OI 630-nm imagers, ionospheric parameters by ionosondes, and mesosphere–lower thermosphere (MLT) gravity waves (MLT-GWs) by OH airglow imagers have been carried out in the equatorial and low-latitude region of Brazil. On 16–17 September 2015, MSTIDs with very fast horizontal phase speeds, propagating toward northeast (NE), were observed over the latitude region of 0–30°S in the afternoon to evening time zone. It was geomagnetically quiet time (Kp: 2–3). An EPB development was observed after one of the MSTIDs crossed the solar terminator at 22:00 UT. Large-scale MLT-GWs with slower phase speeds were also observed both at São João do Cariri (7.5°S, 35.0°W) propagating from southwest (SW) to NE and Cachoeira Paulista (22.7°S, 45.0°W) propagating northward. This is to report on what we consider as a signature of direct seeding of EPBs by an MSTID that was likely induced by a secondary GW from tropospheric deep cloud convections to the south. This study highlights a possible dynamical process from the troposphere to ionosphere via this vertical coupling process over the 2,500 km of horizontal distance.

    DOI: 10.1029/2019JA027566

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  27. The Solar Wind Density Control on the Prompt Penetration Electric Field and Equatorial Electrojet Reviewed

    Nilam B., Ram S. Tulasi, Shiokawa K., Balan N., Zhang Q.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 9 )   2020.9

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    Prompt penetration of convection/overshielding electric fields to equatorial and low latitudes during the southward/northward turnings of interplanetary magnetic field (IMF Bz) have been widely studied in the literature. The other types of penetration electric fields due to sudden changes in the solar wind dynamic pressure, IMF By and during the onset of substorms have also been recently reported. In this paper, we present the exclusive role of solar wind density changes on the prompt equatorial electric field disturbances using the long-term observations of equatorial electrojet (EEJ) from the Indian sector. In response to the sharp increases in the solar wind density, prompt increases/decreases in the EEJ indicating the eastward/westward prompt penetration electric field (PPEF) of ~20 min periods have been consistently observed on the dayside/nightside. The prompt equatorial electric field disturbances of the opposite polarity have also been observed when the density decreases sharply. Further, the polarity of these PPEF disturbances does not show any clear dependency on the direction of IMF Bz and By. This paper is the first report with a statistically significant number of observations on the characteristics of equatorial electric field disturbances in response to the sudden enhancements/decreases in the solar wind density alone on both dayside and nightside. The underlying physical mechanisms for the prompt equatorial electric field disturbances have been discussed in light of enhanced high-latitude convection and additional field-aligned currents due to sudden enhancement of solar wind density.

    DOI: 10.1029/2020JA027869

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  28. Statistical study of EMIC Pc1-Pc2 waves observed at subauroral latitudes Reviewed

    Jong-Woo Kwon, Khan-Hyuk Kim, Ho Jin, Hyuck-Jin Kwon, Geonhwa Jee, Kazuo Shiokawa, Martin Connors

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 205   2020.9

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    Although the occurrence rate of electromagnetic ion cyclotron (EMIC) waves is high in the outer magnetosphere (L > 7), it has been suggested in the past that a steep plasma density gradient region of the plasmapause is a preferred location for the generation of EMIC waves. To examine spectral properties of the EMIC waves occurred near the nominal location of the plasmapause (L = 4-5), we focus on Pc1-Pc2 waves observed at subauroral latitude Athabasca station (magnetic latitude: similar to 62 degrees, and L similar to 4.6). A statistical study of 10,494 wave samples identified from Athabasca data for 2007-2008 reveals the following wave characteristics. (1) Wave frequencies are higher in the postmidnight-to-dawn sector and lower in the late afternoon sector. (2) They mostly appear to be in frequency band between helium and oxygen gyrofrequencies (i.e., He-band) calculated from the dipole field model magnetic field intensity at L = 4.6. (3) The occurrence rate of Pc1-Pc2 waves has a peak in the prenoon sector at 0900-1100 LT under quiet geomagnetic conditions (Kp. 1), but is peaked in the afternoon sector under moderate and disturbed geomagnetic conditions (Kp. 2). (4) The Pc1-Pc2 waves observed at Athabasca were composed of a mixture of left-hand, right-hand, and linearly polarized waves. By comparing previous and recent studies with these observations, we suggest that the subauroral latitude Pc1-Pc2 waves are associated with EMIC waves generated near the plasmapause and discuss the EMIC wave properties in a region of cold and dense plasmas containing heavy ions in the inner magnetosphere.

    DOI: 10.1016/j.jastp.2020.105292

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  29. Spatial Extent of Quasiperiodic Emissions Simultaneously Observed by Arase and Van Allen Probes on 29 November 2018 Reviewed

    C. Martinez‐Calderon, F. Němec, Y. Katoh, K. Shiokawa, C. Kletzing, G. Hospodarsky, O. Santolik, Y. Kasahara, S. Matsuda, A. Kumamoto, F. Tsuchiya, A. Matsuoka, M. Shoji, M. Teramoto, S. Kurita, Y. Miyoshi, M. Ozaki, N. Nishitani, A. V. Oinats, V. I. Kurkin

    Journal of Geophysical Research: Space Physics   Vol. 125 ( 9 )   2020.9

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    DOI: 10.1029/2020ja028126

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA028126

  30. Ionospheric Plasma Density Oscillation Related to EMIC Pc1 Waves Reviewed

    Hyangpyo Kim, Kazuo Shiokawa, Jaeheung Park, Yoshizumi Miyoshi, Yukinaga Miyashita, Claudia Stolle, Khan-Hyuk Kim, Juergen Matzka, Stephan Buchert, Tanja Fromm, Junga Hwang

    GEOPHYSICAL RESEARCH LETTERS   Vol. 47 ( 15 )   2020.8

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    We report the first observation of plasma density oscillations coherent with magnetic Pc1 waves. Swarm satellites observed compressional Pc1 wave activity in the 0.5-3 Hz band, which was coherent with in situ plasma density oscillations. Around the Pc1 event location, the Antarctic Neumayer Station III (L similar to 4.2) recorded similar Pc1 events in the horizontal component while NOAA-15 observed isolated proton precipitations at energies above 30 keV. All these observations support that the compressional Pc1 waves at Swarm are oscillations converted from electromagnetic ion cyclotron (EMIC) waves coming from the magnetosphere. The magnetic field and plasma density oscillate in-phase. We compared the amplitudes of density and magnetic field oscillations normalized to background values and found that the density power is much larger than the magnetic field power. This difference cannot be explained by a simple magnetohydrodynamic (MHD) model, although steep horizontal/vertical gradients of background ionospheric density can partly reconcile the discrepancy.

    DOI: 10.1029/2020GL089000

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  31. Long-Lasting Ground-Satellite High Coherence of Compressional Dayside Pc3-Pc4 Pulsations Reviewed

    Gi-Jeong Kim, Khan-Hyuk Kim, Hyuck-Jin Kwon, Kazuo Shiokawa, Kazue Takahashi, Junga Hwang

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 8 )   2020.8

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    We present observations of broadband (similar to 10-50 mHz) Pc3-Pc4 waves on 4 January 2014. The waves were detected on the dayside simultaneously in a compressional component (delta B-z) at the Radiation Belt Storm Probes A (RBSP-A) in the inner magnetosphere and in the north-south component (delta H) on the ground at a low-latitude Bohyun (BOH) station (L = 1.3) during an interval of small interplanetary magnetic field cone angle, suggesting that upstream ultralow frequency (ULF) waves were the source of the magnetospheric Pc3-Pc4 waves. We observed the ground-satellite high coherence between RBSP-A delta B-z and BOH delta H for a prolonged time interval lasting 6.5hr, which has not been reported previously, during which RBSP-A was on the inbound and outbound legs moving from L = similar to 3.3 to similar to 6.3. In order to understand the spatial mode structure of the compressional waves, we examined the ground-satellite cross phase for the high-coherence interval and found that the waves observed in and out of the plasmasphere propagated earthward at the average fast-mode speed of similar to 700-1,000km/s. We also observed cross-phase values smoothly changing with the radial distance of the spacecraft across the plasmapause. This indicates that the presence of the plasmapause has little effect on our fast-mode waves propagating into the inner magnetosphere and to the ground low-latitude station.

    DOI: 10.1029/2020JA028074

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  32. Asymmetric Development of Auroral Surges in the Northern and Southern Hemispheres Reviewed

    Uchida H.A., Kataoka R., Kadokura A., Murase K., Yukimatu A.S., Miyoshi Y., Shiokawa K., Ebihara Y., Hosokawa K., Matsuoka A., Kurita S., Fujita S., Shinohara I.

    Geophysical Research Letters   Vol. 47 ( 13 )   2020.7

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    Simultaneous eastward and westward traveling surges were observed at Tjörnes, Iceland, and Syowa station, Antarctica, respectively. Several remarkable differences were identified. (1) The position of the initial bright spot was shifted by 1.7 to 2.3 MLT between both hemispheres. (2) The surges differ in traveling speed between the eastward traveling surge (6.5 km s−1) and the westward traveling surge (1.3 km s−1). (3) The Arase satellite was located on a geomagnetic field line connecting both ground stations and observed a significant excess in westward component of the magnetic field, which is consistent with the large shifts of the initial bright spots in both hemispheres. (4) The background Hall current flows eastward (Northern Hemisphere) and westward (Southern Hemisphere). The observed north-south asymmetry of the traveling surges suggests that the ionosphere can play an essential role in controlling the fundamental spatiotemporal development of auroras in both hemispheres.

    DOI: 10.1029/2020GL088750

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  33. Dilatory and Downward Development of 3-m Scale Irregularities in the Funnel-Like Region of a Rapidly Rising Equatorial Plasma Bubble Reviewed

    S. Tulasi Ram, K. K. Ajith, T. Yokoyama, M. Yamamoto, K. Hozumi, K. Shiokawa, Y. Otsuka, G. Li

    Geophysical Research Letters   Vol. 47 ( 13 )   2020.7

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    The equatorial plasma bubbles, once developed, grow nonlinearly into topside ionosphere, and simultaneous secondary instabilities lead to the development of shorter scale irregularities. The altitudinal growth and generation of smaller scale irregularities determine the spatio-temporal occurrence and the intensity of ionospheric scintillations at wide spectrum of radio waves and have significant implications on the GNSS/Satellite Based Augmentation Systems. In this letter, we present a unique equatorial plasma bubble observation from equatorial atmosphere radar that provides hitherto undisclosed evidence for the smaller (3-m) scale irregularities initially developing at higher altitudes and subsequently developing to lower altitudes in a narrow funnel-like structure. The responsible mechanisms for early development of shorter scale irregularities in the topside and their subsequent development at lower altitudes are discussed in light of difference between the time scales of altitudinal growth and cascading rate of secondary instabilities through high-resolution bubble model simulations.

    DOI: 10.1029/2020GL087256

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  34. Arase observation of the source region of auroral arcs and diffuse auroras in the inner magnetosphere Reviewed

    K. Shiokawa, M. Nosé, S. Imajo, Y. Tanaka, Y. Miyoshi, K. Hosokawa, M. Connors, M. Engebretson, Y. Kazama, S.‐Y. Wang, S. W. Y. Tam, Tzu‐Fang Chang, Bo‐Jhou Wang, K. Asamura, S. Kasahara, S. Yokota, T. Hori, K. Keika, Y. Kasaba, M. Shoji, Y. Kasahara, A. Matsuoka, I. Shinohara

    Journal of Geophysical Research: Space Physics   Vol. 125 ( 8 )   2020.7

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    DOI: 10.1029/2019ja027310

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  35. Severe Magnetic Fluctuations in the Near-Earth Magnetotail: Spectral Analysis and Dependence on Solar Activity Reviewed

    Heqiucen Xu, Kazuo Shiokawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 7 )   2020.7

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    Magnetic fluctuations in the near-Earth magnetotail are an important signature of substorm onset. In a previous statistical study, we reported their occurrence rates, spatial distributions, and relationship with plasma flows. In the present study, we investigated their spectral properties using 11 years of measurements from the Time History of Events and Macroscale Interactions during Substorms mission for 2008-2018. We found 10,848 severe magnetic fluctuation events with sigma(B)/(B) over bar) > 0.5, where sigma(B) and (B) over bar are the standard deviation and average, respectively, of the magnetic field intensity for the local proton gyroperiod. The occurrence rates of severe magnetic fluctuations show no clear dependence on the F-10.7 index in one solar cycle. We extracted 36 dipolarization events with severe magnetic fluctuations. In the power spectral density (PSD) of the magnetic fluctuations during dipolarizations, the steepness of the spectral slope increased with increasing frequency in almost all the events. The average PSDs are shown sorted by (a) distance to the neutral sheet and (b) ambient magnetic field intensity. In all groups, the slopes of the average PSDs increased abruptly from below similar to 10(-1.3) Hz (0.05 Hz) to above similar to 10(-1.3) Hz, which is close to the gyrofrequency of O+ ions. It is the first time that a change of slope near the proton gyrofrequency (frequency range: 0.05-1 Hz) was found in cases of larger ambient magnetic field intensity, implying that the magnetic fluctuations were relatively strong near the proton gyrofrequency. These results suggest that the magnetic fluctuations contribute to the nonmagnetohydrodynamic effect in the ion motion.

    DOI: 10.1029/2020JA027834

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  36. Asymmetric Development of Auroral Surges in the Northern and Southern Hemispheres Reviewed International journal

    Herbert Akihito Uchida, Ryuho Kataoka, Akira Kadokura, Kiyoka Murase, Akira Sessai Yukimatu, Yoshizumi Miyoshi, Kazuo Shiokawa, Yusuke Ebihara, Keisuke Hosokawa, Ayako Matsuoka, S. Kurita, Shigeru Fujita, I. Shinohara

    Geophys. Res. Lett.   Vol. 47   2020.6

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  37. Modulation of Pc1 Wave Ducting by Equatorial Plasma Bubble Reviewed

    Hyangpyo Kim, Kazuo Shiokawa, Jacheung Park, Yoshizumi Miyoshi, Junga Hwang, Akira Kadokura

    GEOPHYSICAL RESEARCH LETTERS   Vol. 47 ( 9 )   2020.5

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    Ducting Pc1 waves are observed over a wide latitudinal range by the low-Earth orbit satellites as compressional mode. In this paper, we present the first observation of the modulation of ducting Pc1 waves by equatorial plasma bubbles (EPBs) based on the Swarm satellites. We show two ducting Pc1 events propagating across EPBs that occurred on 7 April 2016 and on 27 September 2017. We found that the EPBs modulate the Pc1 wave propagation by setting up reflection boundaries and leakage holes in the ionospheric waveguide. We also found that changes of Pc1 wave intensities generally follow the electron density variation and that the intensity is stronger at higher density region. From the comparison between Swarm-A and Swarm-C observations, we conclude that ionospheric plasma plays an important role for Pc1 waveguide even though their density is significantly low in EPBs.

    DOI: 10.1029/2020GL088054

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  38. Observations of equatorial plasma bubbles using a low-cost 630.0-nm all-sky imager in Ishigaki Island, Japan Reviewed

    Keisuke Hosokawa, Kohei Takami, Susumu Saito, Yasunobu Ogawa, Yuichi Otsuka, Kazuo Shiokawa, Chia-Hung Chen, Chien-Hung Lin

    EARTH PLANETS AND SPACE   Vol. 72 ( 1 )   2020.5

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    Here, we introduce a low-cost airglow imaging system developed for observing plasma bubble signatures in 630.0-nm airglow emission from the F region of the ionosphere. The system is composed of a small camera, optical filter, and fish-eye lens, and is operated using free software that automatically records video from the camera. A pilot system was deployed in Ishigaki Island in the southern part of Japan (Lat 24.4, Lon 124.4, Mlat 19.6) and was operated for similar to 1.5 years from 2014 to 2016 corresponding to the recent solar maximum period. The pilot observations demonstrated that it was difficult to identify the plasma bubble signature in the raw image captured every 4 s. However, the quality of the image could be improved by reducing the random noise of instrumental origin through an integration of 30 consecutive raw images obtained in 2 min and further by subtracting the 1-h averaged background image. We compared the deviation images to those from a co-existing airglow imager of OMTIs, which is equipped with a back-illuminated cooled CCD camera with a high quantum efficiency of similar to 90%. It was confirmed that the low-cost airglow imager is capable of imaging the spatial structure of plasma bubbles, including their bifurcating traces. The results of these pilot observations in Ishigaki Island will allow us to distribute the low-cost imager in a wide area and construct a network for monitoring plasma bubbles and their space weather impacts on satellite navigation systems.

    DOI: 10.1186/s40623-020-01187-1

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  39. Equatorial Plasma Bubble Zonal Drift Velocity Variations in Response to Season, Local Time, and Solar Activity across Southeast Asia Reviewed

    Sarudin I., Hamid N.S.A., Abdullah M., Buhari S.M., Shiokawa K., Otsuka Y., Yatini C.Y.

    Journal of Geophysical Research: Space Physics   Vol. 125 ( 3 )   2020.3

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    This work investigated the zonal drift velocity, VE, of equatorial plasma bubbles (EPBs) which was calculated from the zonal keogram of the rate of total electron content index obtained using the Global Positioning System data from the Malaysia Real-Time Kinematics GNSS Network over Southeast Asia across the period 2008 until 2013 (498 nights). In general, a long-term study on the VE of EPBs and its dependence on the season, local time, and solar activity over Southeast Asia by using Global Positioning System multipoint receivers has never been conducted before. The case study showed that the VE estimated from Malaysia Real-Time Kinematics GNSS Network was basically within a similar range to that of the 630-nm airglow images obtained at Kototabang, Indonesia. Furthermore, the VE of EPBs was higher during high solar-activity period, which was in line with past studies. The time range of the EPB VE peak is more accurately determined compared to previous studies. In high solar activity conditions, a peak of VE was observed at 2130 LT (equinox), 2200 LT (June solstice), and after 2300 LT (December solstice). After this peak, the EPB VE steadily decreased with time during the equinox and was varied throughout the night during June solstice. Moreover, it was found to differ with time from the evening to the postmidnight period during December solstice.

    DOI: 10.1029/2019JA027521

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  40. Multievent Analysis of Oscillatory Motion of Medium-Scale Traveling Ionospheric Disturbances Observed by a 630-nm Airglow Imager Over Tromsø Reviewed

    Yadav S., Shiokawa K., Oyama S., Otsuka Y.

    Journal of Geophysical Research: Space Physics   Vol. 125 ( 3 )   2020.3

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    We present a comprehensive investigation on the propagation characteristics of duskside medium-scale traveling ionospheric disturbances (MSTIDs) using 630.0-nm airglow emissions over Tromsø (69.6°N, 19.2°E; magnetic latitude: 66.7°N). The unique points of our observation are (1) duskside MSTIDs primarily exhibited eastward motion under quiet conditions but turned to the westward direction associated with geomagnetic disturbances, (2) the westward moving MSTIDs again turned to the eastward direction when the geomagnetic disturbance ceased, (3) the turning of MSTIDs to the westward direction was invariably associated with an increase of the northward component of the magnetic field observed by the local ground-based magnetometers and with the equatorward expansion of the auroral oval, and (4) the Super Dual Auroral Radar Network convection maps revealed that the location of Tromsø was inside (outside) the duskside convection cell during the time of appearance of westward (eastward) moving MSTIDs. The average eastward and westward velocities of MSTIDs were ~25–80 and ~40–140 m/s, respectively. The Doppler shift measurement of the 630-nm airglow by a Fabry-Perot interferometer at Tromsø showed that northeastward winds were predominant during the appearance of eastward moving MSTIDs. These experimental evidences suggest that the oscillatory motion of MSTIDs over high latitudes is driven by the convection electric field. The MSTIDs tend to move eastward under geomagnetically quiet conditions but show westward motion under the influence of convection electric field associated with auroral activities in the duskside of two-cell convection pattern.

    DOI: 10.1029/2019JA027598

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  41. Development of low-cost multi-wavelength imager system for studies of aurora and airglow Reviewed

    Y. Ogawa, Y. Tanaka, A. Kadokura, K. Hosokawa, Y. Ebihara, T. Motoba, B. Gustavsson, U. Brändström, Y. Sato, S. Oyama, M. Ozaki, T. Raita, F. Sigernes, S. Nozawa, K. Shiokawa, M. Kosch, K. Kauristie, C. Hall, S. Suzuki, Y. Miyoshi, A. Gerrard, H. Miyaoka, R. Fujii

    Polar Science   Vol. 23   2020.3

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    © 2019 Elsevier B.V. and NIPR This paper introduces a new system that can monitor aurora and atmospheric airglow using a low-cost Watec monochromatic imager (WMI) equipped with a sensitive camera, a filter with high transmittance, and the non-telecentric optics. The WMI system with 486-nm, 558-nm, and 630-nm band-pass filters has observable luminosity of about ~200–4000 Rayleigh for 1.07-sec exposure time and about ~40–1200 Rayleigh for 4.27-sec exposure time, for example. It is demonstrated that the WMI system is capable of detecting 428-nm auroral intensities properly, through comparison with those measured with a collocated electron-multiplying charge-coupled device (EMCCD) imager system with narrower band-pass filter. The WMI system has two distinct advantages over the existing system: One makes it possible to reduce overall costs, and the other is that it enables the continuous observation even under twilight and moonlight conditions. Since 2013 a set of multi-wavelength WMIs has been operating in northern Scandinavia, Svalbard, and Antarctica to study meso- and large-scale aurora and airglow phenomena. Future development of the low-cost WMI system is expected to provide a great opportunity for constructing a global network for multi-wavelength aurora and airglow monitoring.

    DOI: 10.1016/j.polar.2019.100501

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  42. Fine-Scale Visualization of Aurora in a Wide Area Using Color Digital Camera Images From the International Space Station Reviewed

    Sota Nanjo, Yuta Hozumi, Keisuke Hosokawa, Ryuho Kataoka, Yoshizumi Miyoshi, Shin-ichiro Oyama, Mitsunori Ozaki, Kazuo Shiokawa, Satoshi Kurita

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 3 )   2020.3

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    The full-color photographs of aurora have been taken with digital single-lens reflex cameras mounted on the International Space Station (ISS). Since these photographs do not have accurate time and geographical information, in order to use them as scientific data, it is necessary to calibrate the imaging parameters (such as looking direction and angle of view of the camera) of the photographs. For this purpose, we calibrated the imaging parameters using a city light image taken from the Defense Meteorological Satellite Program satellite following the method of Hozumi et al. (2016, https://doi.org/10.1186/s40623-016-0532-z). We mapped the photographs onto the geographic coordinate system using the calibrated imaging parameters. To evaluate the accuracy of the mapping, we compared the aurora taken simultaneously from ISS and ground. Comparing the spatial structure of discrete aurora and the temporal variation of pulsating aurora, the accuracy of the data set is less than 0.3 s in time and less than 5 km in space in the direction perpendicular to the looking direction of the camera. The generated data set has a wide field of view (similar to 1,100 x 900 km), and their temporal resolution is less than 1 s. Not only that, the field of view can sweep a wide area (similar to 3,000km in longitude) in a short time (similar to 10 min). Thus, this new imaging capability will enable us to capture the evolution of fine-scale spatial structure of aurora in a wide area.

    DOI: 10.1029/2019JA027729

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  43. ULF Modulation of Energetic Electron Precipitations Observed by VLF/LF Radio Propagation Invited Reviewed

    Takuya Miyashita, Hiroyo Ohya, Fuminori Tsuchiya, Asuka Hirai, Mitsunori Ozaki, Kazuo Shiokawa, Yoshizumi Miyoshi, Nozomu Nishitani, Mariko Teramoto, Martin Connors, Simon G. Shepherd, Yoshiya Kasahara, Atsushi Kumamoto, Masafumi Shoji, Iku Shinohara, Hiroyuki Nakata, Toshiaki Takano

    Radio Science Bulletin     2020.3

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  44. Wavenumber Spectra of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances Based on More Than 10-Year Airglow Images in Japan, Russia, and Canada Reviewed

    Satoshi Tsuchiya, Kazuo Shiokawa, Yuichi Otsuka, Takuji Nakamura, Mamoru Yamamoto, Martin Connors, Ian Schofield, Boris Shevtsov, Igor Poddelsky

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 3 )   2020.3

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    We have studied atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) by applying three-dimensional spectral analysis technique to 557.7- and 630.0-nm airglow images at Shigaraki (SGK) (35 degrees N, 136 degrees E, 1999-2017) and Rikubetsu (RIK) (44 degrees N, 144 degrees E, 1999-2017), Japan, Athabasca (ATH), Canada, (55 degrees N, 247 degrees E, 2005-2017), and Magadan (MGD), Russia (60 degrees N, 151 degrees E, 2008-2017), focusing on their horizontal wavenumber spectra. For the AGWs in 557.7-nm images, the power spectra in summer are stronger than in other seasons, probably due to stronger tropospheric convection. The highest energy content of the waves are mostly at wavelengths between 20 and 300 km at MGD, ATH, and RIK, while it is above 200 km at SGK. The largest power spectral density is obtained at RIK at wavelengths of 30-100 km and then ATH. The slopes of the horizontal wavenumber spectra varies from -2.77 to -3.22. From the MSTIDs in 630.0-nm images, the power spectra in summer at RIK and SGK are stronger than those in other seasons regardless of solar activity. The power spectra in solar quiet time are stronger than those in solar active time at all four stations. These features can be explained by the Perkins instability with coupling between sporadic E and F layers. The spectral slope decreases with increasing latitudes. Weak positive correlations were obtained between the daily wave power of AGWs in 557.7-nm images and MSTIDs in 630.0-nm images, suggesting that the MSTIDs in the thermosphere may be partially generated by the AGWs from the mesopause region.Plain Language Summary In this paper we study atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed at four stations in Japan, Canada, and Russia, in 557.7- and 630.0-nm airglow images over more than 10 years. The 557.7-nm airglow has an emission layer at altitudes of 90-100 km (mesopause region). The waves seen in the 557.7-nm airglow images mainly indicates AGWs. The 630.0-nm airglow has an emission layer at altitudes of 200-300 km (bottomside ionosphere). The waves seen in the 630.0-nm airglow images mainly indicates MSTIDs in the ionosphere. The AGWs in the mesopause region are the main driver of global atmospheric circulation in the middle atmosphere. The MSTIDs in the bottomside ionosphere are one of the causes of the satellite positioning error. We show typical energy content, propagation direction, and wavelengths of these waves at these two altitudes and discuss possible reason of the observed characteristics. These results contribute to our understanding of generation and propagation of AGWs and MSTIDs in the upper atmosphere.

    DOI: 10.1029/2019JA026807

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  45. Multiple time-scale beats in aurora: precise orchestration via magnetospheric chorus waves Reviewed

    Hosokawa K., Miyoshi Y., Ozaki M., Oyama S.I., Ogawa Y., Kurita S., Kasahara Y., Kasaba Y., Yagitani S., Matsuda S., Tsuchiya F., Kumamoto A., Kataoka R., Shiokawa K., Raita T., Turunen E., Takashima T., Shinohara I., Fujii R.

    Scientific reports   Vol. 10 ( 1 )   2020.2

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    The brightness of aurorae in Earth's polar region often beats with periods ranging from sub-second to a few tens of a second. Past observations showed that the beat of the aurora is composed of a superposition of two independent periodicities that co-exist hierarchically. However, the origin of such multiple time-scale beats in aurora remains poorly understood due to a lack of measurements with sufficiently high temporal resolution. By coordinating experiments using ultrafast auroral imagers deployed in the Arctic with the newly-launched magnetospheric satellite Arase, we succeeded in identifying an excellent agreement between the beats in aurorae and intensity modulations of natural electromagnetic waves in space called "chorus". In particular, sub-second scintillations of aurorae are precisely controlled by fine-scale chirping rhythms in chorus. The observation of this striking correlation demonstrates that resonant interaction between energetic electrons and chorus waves in magnetospheres orchestrates the complex behavior of aurora on Earth and other magnetized planets.

    DOI: 10.1038/s41598-020-59642-8

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  46. Multiple time-scale beats in aurora: precise orchestration via magnetospheric chorus waves Reviewed

    Hosokawa, K., Y. Miyoshi, M. Ozaki, S.-I. Oyama, Y. Ogawa, S. Kurita, Y. Kasahara, Y. Kasaba, S. Yagitani, S. Matsuda, F. Tsuchiya, A. Kumamoto, R. Kataoka, K. Shiokawa, T. Raita, E. Turunen, T. Takashima, I. Shinohara, R. Fujii

    Sci. Rep.   Vol. 10   2020.2

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  47. Probing afternoon detached aurora and high-latitude trough based on DMSP observations Reviewed

    Su Zhou, Kazuo Shiokawa, Igor Poddelsky, Yuqing Chen, Jin Zhang

    ADVANCES IN SPACE RESEARCH   Vol. 65 ( 1 ) page: 214 - 220   2020.1

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    The present work displays the observations of an afternoon detached aurora along with ionospheric high-latitude trough. The event was observed by DMSP F17 on 19 September 2014. The afternoon detached aurora was isolated from the auroral oval and was located between 12:00-18:00 magnetic local time (MLT) and 65-70 degrees geomagnetic latitude (MLAT). Particle observations indicate that the afternoon detached aurora was produced by energetic ring current ions with energies above similar to 10 keV where the main ion energy was likely to be above the upper limit of DMSP measurement (similar to 30 keV). Magnetometer observation from the ground implies that the energetic ions were likely scattered by EMIC waves. Both the detached aurora and the auroral oval are found to be well inside the high-latitude trough with MLAT between similar to 64 degrees and similar to 76 degrees (68-80 degrees GLAT). The auroral oval corresponds to a westward (sunward) plasma drift. It is expected that the westward drift transports the low-density plasma in the nightside toward the dayside, leading to the high-latitude trough formation. The afternoon detached aurora was well equatorward of the high-latitude trough, and the corresponding plasma drift was nearly zero. The plasma associated with the detached aurora is expected to be stagnant, and broaden the high-latitude trough equatorward. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.asr.2019.10.003

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  48. Conjugate Observations of Dayside and Nightside VLF Chorus and QP Emissions Between Arase (ERG) and Kannuslehto, Finland Reviewed

    Claudia Martinez-Calderon, Yuto Katoh, Jyrki Manninen, Yoshiya Kasahara, Shoya Matsuda, Atsushi Kumamoto, Fuminori Tsuchiya, Ayako Matsuoka, Masafumi Shoji, Mariko Teramoto, Iku Shinohara, Kazuo Shiokawa, Yoshizumi Miyoshi

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 125 ( 1 )   2020.1

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    We compare for the first time two conjugate events showing simultaneous very low frequency (VLF) wave observations between the same ground station and spacecraft, at different geomagnetic conditions and on opposite sides of the magnetosphere. Waves were observed at Kannuslehto (MLAT = 64.4 degrees N, L = 5.46), Finland, and on board Arase (Exploration of energization and Radiation in Geospace, ERG) in the inner magnetosphere. Case 1 on 28 March 2017 shows quasiperiodic (QP) emissions and chorus simultaneously observed on the postmidnight side during the recovery phase of a storm, with sustained high solar wind speed and AE index. Case 2 on 30 November 2017 shows clear one-to-one correspondence of QP elements on the noonside during geomagnetic quiet time (Dst > 10 nT and AE < 100 nT). We present the characteristics of both cases, focusing on coherence and spatial extent of the waves, electron density, and magnetic field variations. We report that the magnetic field gradient plays a role in the changes of spectral features of the waves.

    DOI: 10.1029/2019JA026663

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  49. Capability of Geomagnetic Storm Parameters to Identify Severe Space Weather Reviewed

    Balan N., Zhang Q.H., Xing Z., Skoug R., Shiokawa K., Lühr H., Ram S.T., Otsuka Y., Zhao L.

    Astrophysical Journal   Vol. 887 ( 1 )   2019.12

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    The paper investigates the capability of geomagnetic storm parameters in the disturbance storm-time (Dst), Kp, and AE indices to distinguish between severe space weather (SvSW) that causes the reported electric power outages and/or telecommunication failures and normal space weather (NSW) that does not cause these severe effects in a 50 yr period (1958-2007). The parameters include the storm intensities DstMin (minimum Dst during the main phase, MP, of the storm), (dDst/dt)MPmax, Kpmax, and AEmax. In addition, the impulsive parameter is derived for the storms that are automatically identified in the Kyoto Dst and USGS Dst.∫TMP| DstMP| dt is the integral of the modulus of the Dst from onset of the MP (MPO) to the DstMin. T MP is the MP duration from MPO to DstMin. The corresponding mean values KpMP and AEMP are also calculated. Regardless of the significant differences in the storm parameters between the two Dst indices, the IpsDst in both indices seems to identify four of the five SvSW events (and the Carrington event) in more than 750 NSW events that have been reported to have occurred in 1958-2007, while all other parameters separate one or two SvSWs from the NSWs. Using the Kyoto IpsDst threshold of -250 nT, we demonstrate a 100% true SvSW identification rate with only one false NSW. Using the false NSW event (1972 August 4), we investigate whether using a higher resolution Dst might result in a more accurate identification of SvSWs. The mechanism of the impulsive action leading to large IpsDst and SvSW involves the coincidence that the fast interplanetary coronal mass ejection velocity V contains its shock (or front) velocity ΔV and large interplanetary magnetic field Bz southward covering ΔV.

    DOI: 10.3847/1538-4357/ab5113

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  50. Three Different Episodes of Prompt Equatorial Electric Field Perturbations Under Steady Southward IMF Bz During St. Patrick's Day Storm Reviewed

    S. Tulasi Ram, B. Nilam, N. Balan, Q. Zhang, K. Shiokawa, D. Chakrabarty, Z. Xing, K. Venkatesh, B. Veenadhari, A. Yoshikawa

    Journal of Geophysical Research: Space Physics   Vol. 124 ( 12 ) page: 10428 - 10443   2019.12

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    Three different episodes of prompt penetration electric field (PPEF) disturbances are observed during the main phase of the St. Patrick's Day storm on 17 March 2015 under steady southward interplanetary magnetic field (IMF) Bz conditions unlike the conventional PPEF associated with southward or northward turnings of IMF Bz. These PPEF events took place during the period when strong disturbance dynamo fields are prevailing in the background. The first event is triggered by a solar wind dynamic pressure pulse that caused a sharp eastward PPEF and strong enhancement of equatorial electrojet current in Brazilian dayside. The second event caused another short but strong westward PPEF on dayside due to the reversal of IMF By from duskward to dawnward under steady IMF Bz. The third event caused a longer eastward PPEF in association with a solar wind dynamic pressure pulse followed by the onset of a substorm, which has led to strong enhancement of equatorial electrojet, quick rejuvenation and symmetric redistribution of equatorial ionization anomaly in the Brazilian sector. The signatures of the PPEF with opposite polarity and smaller magnitudes are also observed in the Asian sector on the nightside. The possible mechanisms for the observed PPEF events under steady IMF Bz are discussed in terms of changes in the high-latitude field-aligned currents and reconfiguration of high-latitude convection fields using Active Magnetosphere and Planetary Electrodynamics Response Experiment and Super Dual Auroral Radar Network high-frequency radar observations.

    DOI: 10.1029/2019JA027069

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  51. A Neural Network-Based Ionospheric Model Over Africa From Constellation Observing System for Meteorology, Ionosphere, and Climate and Ground Global Positioning System Observations Reviewed

    Daniel Okoh, Gopi Seemala, Babatunde Rabiu, John Bosco Habarulema, Shuanggen Jin, Kazuo Shiokawa, Yuichi Otsuka, Malini Aggarwal, Jean Uwamahoro, Patrick Mungufeni, Bolaji Segun, Aderonke Obafaye, Nada Ellahony, Chinelo Okonkwo, Mpho Tshisaphungo, Dadaso Shetti

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 12 ) page: 10512 - 10532   2019.12

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    The first regional total electron content (TEC) model over the entire African region (known as AfriTEC model) using empirical observations is developed and presented. Artificial neural networks were used to train TEC observations obtained from Global Positioning System receivers, both on ground and onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate satellites for the African region from years 2000 to 2017. The neural network training was implemented using inputs that enabled the networks to learn diurnal variations, seasonal variations, spatial variations, and variations that are connected with the level of solar activity, for quiet geomagnetic conditions (-20 nT <= Dst <= 20 nT). The effectiveness of three solar activity indices (sunspot number, solar radio flux at 10.7-cm wavelength [F10.7], and solar ultraviolet [UV] flux at 1 AU) for the neural network trainings was tested. The F10.7 and UV were more effective, and the F10.7 was used as it gave the least errors on the validation data set used. Equatorial anomaly simulations show a reduced occurrence during the June solstice season. The distance of separation between the anomaly crests is typically in the range from about 11.5 +/- 1.0 degrees to 16.0 +/- 1.0 degrees. The separation is observed to widen as solar activity levels increase. During the December solstice, the anomaly region shifts southwards of the equinox locations; in year 2012, the trough shifted by about 1.5 degrees and the southern crest shifted by over 2.5 degrees.

    DOI: 10.1029/2019JA027065

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  52. Longitudinal Extent of Magnetospheric ELF/VLFWaves using Multipoint PWING Ground Stations at Subauroral Latitudes Reviewed

    Yuhei Takeshita, Kazuo Shiokawa, Mitsunori Ozaki, Jyrki Manninen, Shin-Ichiro Oyama, Martin Connors, Dmitry Baishev, Vladimir Kurkin, Alexey Oinats

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 12 ) page: 9881 - 9892   2019.12

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    Magnetospheric extremely low frequency/very low frequency (ELF/VLF) waves are plasma waves emitted from high-energy electrons in the magnetosphere. These waves have received much attention, as they contribute to the acceleration and loss of relativistic electrons in the radiation belts through wave-particle interactions. The longitudinal extent of ELF/VLF waves has not been well-understood, although the extent is important in quantitative evaluation of relativistic electron variations. In this study, we analyzed data from continuous ground-based simultaneous observations of ELF/VLF waves over a 2-month period in November and December of 2017, using six loop antennas located at roughly equal intervals around the north geomagnetic pole at similar to 60 degrees. magnetic latitudes. We estimated the longitudinal extent of magnetospheric ELF/VLF waves based on their occurrence rate. Our results showed that the ELF/VLF wave occurrence rate differed by twofold to threefold, depending on the longitudes of the observation sites. We explain this difference in terms of longitudinal differences in the ionosphere's magnetic field intensity, possibly due to the electron loss that occurs during the bounce motion at longitudes of small magnetic field intensity. Based on our statistical analysis, we estimated the typical longitudinal extent of ELF/VLF waves as similar to 76 degrees. Time series analysis results showed that the large longitudinal extent of the ELF/VLF waves occurs frequently during the main phase of geomagnetic storms and is also associated with substorms represented by the auroral electrojet index.

    DOI: 10.1029/2019JA026810

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  53. IpsDst of Dst Storms Applied to Ionosphere-Thermosphere Storms and Low-Latitude Aurora Reviewed

    Balan N., Zhang Q.H., Shiokawa K., Skoug R., Xing Z., Tulasi Ram S., Otsuka Y.

    Journal of Geophysical Research: Space Physics   Vol. 124 ( 11 ) page: 9552 - 9565   2019.11

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    Conventionally, the minimum value of Dst (DstMin) and maximum values of Kp and AE (Kpmax and AEmax) representing the geomagnetic storm intensities have been used for investigating space weather in Earth's environment. The present paper uses the derived parameters (IpsDst, IpsKp, and IpsAE) giving the mean values of Dst, Kp, and AE during the main phase (MP) of Dst storms for investigating ionosphere-thermosphere storms and low-latitude (630 nm) aurora. The derived parameters (IpsDst, IpsKp, and IpsAE) representing the impulsive strength of geomagnetic storms seem to have more systematic dependence among themselves than among the intensities (DstMin, Kpmax, and AEmax). The ionosphere-thermosphere storms observed by the CHAMP (Challenging Minisatellite Payload) satellite and low-latitude auroras observed by optical imagers are much more intense during high impulsive storms than high intensity storms. In a statistical sense, over 175 positive ionospheric storms (△NmF2) observed in 1985–2005 and the intensity of 20 red auroras observed in 1989–2004 at midlatitudes correlate better with the impulsive parameters than the intensity parameters, with the best correlation being with IpsDst. The mechanism of the impulsive action (high-energy input over a short duration) leading to large IpsDst arises from the impact of fast solar storms (interplanetary coronal mass ejections) with large IMF Bz southward at their front (or shock). The impulsive action results in bright low-latitude auroras and strong ionosphere-thermosphere storms.

    DOI: 10.1029/2019JA027080

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  54. Statistical Study of Auroral/Resonant-Scattering 427.8-nm Emission Observed at Subauroral Latitudes Over 14 Years Reviewed

    Shiokawa K., Otsuka Y., Connors M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 11 ) page: 9293 - 9301   2019.11

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    Auroral emission at 427.8-nm from N2+ ions is caused by precipitation of energetic electrons, or by resonant scattering of sunlight by auroral N2+ ions. The latter often causes impressive purple aurora at high altitudes. However, statistical characteristics of auroral 427.8-nm emission have not been well studied. In this paper we report occurrence characteristics of high 427.8-nm emission intensities (more than 100 R) at subauroral latitudes, based on measurements by a filter-tilting photometer over 14 years (2005–2018) at Athabasca, Canada (magnetic latitude: ~62°). We divided the data set into solar elevation angles (θs) more than and less than −24° (shadow height of sunlight: 600 km) to separate the 427.8-nm emissions caused by resonant scattering of sunlight and those excited by auroral electrons, respectively. The occurrence rate of 427.8-nm emissions of more than 100 R is 10.6% and 7.65% for θs more than and less than −24°, respectively, confirming that resonant scattering of sunlight by N2+ ions is a cause of the strong 427.8-nm emissions of more than 100 R in the sunlit ionosphere. The occurrence rate is high in the postmidnight sector and increases with increasing geomagnetic activity, solar wind speed, and density. The occurrence rate is lowest in winter. A high occurrence rate was observed in 2015–2018, during the declining phase of the 11-year solar activity. Superposed epoch analysis indicates that the 427.8-nm emission exceeds 100 R when solar wind speed increases and solar wind density concurrently decreases, though the standard deviation of the data is rather large.

    DOI: 10.1029/2019JA026704

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  55. High-latitude thermospheric wind study using a Fabry-Perot interferometer at Tromso in Norway: averages and variations during quiet times Reviewed

    Heqiucen Xu, Kazuo Shiokawa, Shin-ichiro Oyama, Satonori Nozawa

    EARTH PLANETS AND SPACE   Vol. 71 ( 1 )   2019.10

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    The average winds in the thermosphere during geomagnetically quiet times are important because they provide a baseline wind in the upper atmosphere, but they remain insufficiently understood at high latitudes. This paper reports the first direct ground-based wind measurements of the quiet-time thermospheric wind pattern at Tromso in Norway using 2009-2015 data from a Fabry-Perot interferometer. We analyzed red-line wind measurements (630.0 nm; altitude: 200-300 km). On average, the zonal wind shows a decrease of eastward wind compared with diurnal tidal wind before midnight. A maximum speed of 100 m/s occurs at both the dusk and dawn sides. The meridional wind has a diurnal tide structure with a minimum value of - 130 m/s around midnight. We also found occasional large wind deviations (> 100 m/s) from the averages, even during geomagnetically quiet times. We suggest that these large wind deviations are caused by the plasma convection associated with weak substorm activities with auroral electrojet (AE) index values of less than 100 nT that occurred at local times different from that at Tromso.

    DOI: 10.1186/s40623-019-1093-8

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  56. Direct comparison between magnetospheric plasma waves and polar mesosphere winter echoes in both hemispheres Reviewed International journal

    Tanaka, Y.-M, T. Nishiyama, A. Kadokura, M. Ozaki, K. Shiokawa, S. Oyama, M. Nosé, T. Nagatsuma, M. Tsutsumi, K. Nishimura, K. Sato, Y. Miyoshi, Y. Kasahara, A. Kumamoto, F. Tsuchiya, M. Hikishima, S. Matsuda, A. Matsuoka, M. Shinohara, A. Fujimoto, M. Teramoto, R. Nomura, R. Kataoka, A. Sessai Yukimatu

    J. Geophys. Res. (SPA)   Vol. 124 ( 11 ) page: 9626 - 9639   2019.10

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    We present the first and direct comparison between magnetospheric plasma waves and polar mesosphere winter echoes (PMWE) simultaneously observed by the conjugate observation with Arase satellite and high‐power atmospheric radars in both hemispheres, namely, the Program of the Antarctic Syowa Mesosphere, Stratosphere, and Troposphere/Incoherent Scatter Radar at Syowa Station (SYO; −69.00°S, 39.58°E), Antarctica, and the Middle Atmosphere Alomar Radar System at Andøya (AND; 69.30°N, 16.04°E), Norway. The PMWE were observed during 03–07 UT on 21 March 2017, just after the arrival of corotating interaction region in front of high‐speed solar wind stream. An isolated substorm occurred at 04 UT during this interval. Electromagnetic ion cyclotron (EMIC) waves and whistler mode chorus waves were simultaneously observed near the magnetic equator and showed similar temporal variations to that of the PMWE. These results indicate that chorus waves as well as EMIC waves are drivers of precipitation of energetic electrons, including relativistic electrons, which make PMWE detectable at 55‐ to 80‐km altitude. Cosmic noise absorption measured with a 38.2‐MHz imaging riometer and low‐altitude echoes at 55–70 km measured with an medium‐frequency radar at SYO also support the relativistic electron precipitation. We suggest a possible scenario in which the various phenomena observed in near‐Earth space, such as magnetospheric plasma waves (EMIC waves and chorus waves), pulsating auroras, cosmic noise absorption, and PMWE, can be explained by the interaction between the high‐speed solar wind containing corotating interaction regions and the magnetosphere.

    DOI: 10.1029/2019JA026891

  57. Three-Dimensional Fourier Analysis of the Phase Velocity Distributions of Mesospheric and Ionospheric Waves Based on Airglow Images Collected Over 10 Years: Comparison of Magadan, Russia, and Athabasca, Canada Reviewed

    Satoshi Tsuchiya, Kazuo Shiokawa, Hatsuki Fujinami, Yuichi Otsuka, Takuji Nakamura, Martin Connors, Ian Schofield, Boris Shevtsov, Igor Poddelskiy

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 10 ) page: 8110 - 8124   2019.10

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    We studied atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) using a three-dimensional spectral analysis technique for airglow images at wavelengths of 557.7 nm (altitude: 90-100 km for AGWs) and 630.0 nm (200-300 km for MSTIDs), obtained from Athabasca (ATH), Canada (55 degrees N, 247 degrees E, 2005-2017), and Magadan (MGD), Russia (60 degrees N, 151 degrees E, 2008-2017), over 10-13 years. The AGW propagation direction in summer was from northwestward to northward in ATH and northeastward in MGD with phase speeds of 20-60 m/s. In winter at ATH, they are more omnidirectional with weak preference from northwestward to southward with a speed less than 40 m/s, while another weaker power exists from northeastward to southeastward from 70 to 120 m/s. In winter at MGD, there was no dominant direction in the phase-velocity spectra with spectral power an order smaller than ATH. We suggest that these AGW characteristics were caused by wind filtering and intensity and locations of tropospheric sources. The MSTIDs at ATH propagated southwestward in spring and winter and northeastward in summer and fall. The MSTIDs at MGD propagated northeastward, eastward, and westward in spring, fall, and winter, respectively, with weaker power than that at ATH. The phase speeds are mostly less than 100 m/s except for fall. The propagation direction tends to change from south-southwestward in the evening to north-northeastward after the midnight at both ATH and MGD. We discuss possible reasons for these MSTID characteristics at high latitudes based on Perkins and E-F coupling instabilities, high-latitude plasma convection, and thermospheric neutral winds.

    DOI: 10.1029/2019JA026783

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  58. Mesoscale Convection Structures Associated With Airglow Patches Characterized Using Cluster-Imager Conjunctions Reviewed

    Goodwin L.V., Nishimura Y., Zou Y., Shiokawa K., Jayachandran P.T.

    Journal of Geophysical Research: Space Physics   Vol. 124 ( 9 ) page: 7513 - 7532   2019.9

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    Polar cap ionospheric plasma flow studies often focus on large-scale averaged properties and neglect the mesoscale component. However, recent studies have shown that mesoscale flows are often found to be collocated with airglow patches. These mesoscale flows are typically a few hundred meters per second faster than the large-scale background and are associated with major auroral intensifications when they reach the poleward boundary of the nightside auroral oval. Patches often also contain ionospheric signatures of enhanced field-aligned currents and localized electron flux enhancements, indicating that patches are associated with magnetosphere-ionosphere coupling on open field lines. However, magnetospheric measurements of this coupling are lacking, and it has not been understood what the magnetospheric signatures of patches on open field lines are. The work presented here explores the magnetospheric counterpart of patches and the role these structures have in plasma transport across the open field-line region in the magnetosphere. Using red-line emission measurements from the Resolute Bay Optical Mesosphere Thermosphere Imager, and magnetospheric measurements made by the Cluster spacecraft, conjugate events from 2005 to 2009 show that lobe measurements on field lines connected to patches display (1) electric field enhancements, (2) Region 1 sense field-aligned currents, (3) field-aligned enhancements in soft electron flux, (4) downward Poynting fluxes, and (5) in some cases enhancements in ion flux, including ion outflows. These observations indicate that patches highlight a localized fast flow channel system that is driven by the magnetosphere and propagates from the dayside to the nightside, most likely being initiated by enhanced localized dayside reconnection.

    DOI: 10.1029/2019JA026611

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  59. Thermospheric wind variations observed by a Fabry-Perot interferometer at Tromso, Norway, at substorm onsets Reviewed

    Heqiucen Xu, Kazuo Shiokawa, Shin-ichiro Oyama, Yuichi Otsuka

    EARTH PLANETS AND SPACE   Vol. 71 ( 1 )   2019.8

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    Energy input from the magnetosphere during substorms can strongly affect the high-latitude thermosphere. The ionospheric current caused by thermospheric wind variations may also provide a feedback to the magnetosphere. In this study, we investigate the characteristics of high-latitude thermospheric wind variations at local substorm onsets at Tromso, Norway, as well as the possibility of such feedback mechanism. A Fabry-Perot interferometer (FPI) at Tromso provided wind measurements estimated from the Doppler shift of red-line emission (630.0 nm) of aurora and airglow. We analyzed wind data in 2009 with a time resolution of similar to 13 min. We first carefully identified the onset times of isolated local substorms at Tromso and extracted four wind measurements from red-line emission. All these events showed increases of eastward components at local substorm onsets. For northward components, these events showed decreases except for those at midnight. The observed wind variations at local substorm onsets were less than 49 m/s. These values are much smaller than the typical plasma convection speed in the auroral zone. We speculate that the ionospheric current caused by thermospheric wind variations at local substorm onsets does not provide strong feedback to the development of substorm expansion phase in the magnetotail. We discuss the possible causes of these wind variations in the context of plasma convection, diurnal tides, and arc-associated electric field.

    DOI: 10.1186/s40623-019-1072-0

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  60. Multi-instrument Observation of Nonlinear EMIC-Driven Electron Precipitation at sub–MeV Energies Reviewed

    Hendry A., Santolik O., Kletzing C., Rodger C., Shiokawa K., Baishev D.

    Geophysical Research Letters   Vol. 46 ( 13 ) page: 7248 - 7257   2019.7

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    In recent years, experimental results have consistently shown evidence of electromagnetic ion cyclotron (EMIC) wave-driven electron precipitation down to energies as low as hundreds of keV. However, this is at odds with the limits expected from quasi-linear theory. Recent analysis using nonlinear theory has suggested energy limits as low as hundreds of keV, consistent with the experimental results, although to date this has not been experimentally verified. In this study, we present concurrent observations from Polar-orbiting Operational Environmental Satellite, Radiation Belt Storm Probes, Global Positioning System, and ground-based instruments, showing concurrent EMIC waves and sub–MeV electron precipitation, and a global dropout in electron flux. We show through test particle simulation that the observed waves are capable of scattering electrons as low as hundreds of keV into the loss cone through nonlinear trapping, consistent with the experimentally observed electron precipitation.

    DOI: 10.1029/2019GL082401

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  61. EMIC waves converted from equatorial noise due to M/Q=2 ions in the plasmasphere: Observations from Van Allen Probes and Arase Reviewed

    Miyoshi, Y, S. Matsuda, S. Kurita, K. Nomura, K. Keika, M. Shoji, N. Kitamura, Y. Kasahara, A. Matsuoka, I. Shinohara, K. Shiokawa, S. Machida, O. Santolik, S. A. Boardsen, R. B. Horne, J. F. Wygant

    Geophys. Res. Lett.   Vol. 46 ( 11 ) page: 5662 - 5669   2019.4

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    DOI: 10.1029/2019GL083024

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  62. Comprehensive Study of Low-Latitude Pi2 Pulsations Using Observations From Multisatellite Swarm Mission and Global Network of Ground Observatories Reviewed

    Neethal Thomas, Kazuo Shiokawa, Geeta Vichare

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 3 ) page: 1966 - 1991   2019.3

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    To understand the spatial features of low-latitude Pi2 (6.6-25 mHz) pulsations, a comprehensive study is carried out for the first time using magnetic field measurements from a global network of low-latitude ground stations (Mlat: +/- 2 degrees - 51 degrees) and the Swarm multisatellites located simultaneously at day and night local times. We have investigated 1-year data from 2014 and found 15 Pi2 events with coherent oscillations at satellite and ground. The Pi2 oscillations in the compressional, toroidal, and poloidal components at satellite and H, D, and Z components at ground are investigated by estimating its coherence, amplitude, and cross phase with respect to midnight ground H variations. The analogous pairs of magnetic field components (satellite compressional with ground H and satellite toroidal with ground D) above and below the ionosphere are found to have identical phase during night and opposite phase during day, indicating the magnetospheric and ionospheric sources for nighttime and daytime Pi2s, respectively. During nighttime, Pi2 oscillations identified in the poloidal component are found to oscillate in phase (out of phase) in the Southern (Northern) Hemisphere. At ground, the phase and amplitude of H showed significant change near the dawn terminator, whereas H oscillates mostly in phase with respect to midnight ground H at other local times. The oscillations in D component have phase reversal near midnight, dawn, dusk, and noon meridians with opposite hemispheres having opposite phase. These Pi2 characteristics observed globally at ground and at the topside ionosphere suggest that the sources for nighttime and daytime low-latitude Pi2s are oscillating field-aligned currents and ionospheric currents, respectively.

    DOI: 10.1029/2018JA026094

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  63. Observations of Low-Latitude Traveling Ionospheric Disturbances by a 630.0-nm Airglow Imager and the CHAMP Satellite Over Indonesia Reviewed

    Aysegul Ceren Moral, Kazuo Shiokawa, Shin Suzuki, Huixin Liu, Yuichi Otsuka, Clara Yoko Yatini

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 3 ) page: 2198 - 2212   2019.3

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    We report the first comparison of ground and satellite measurements of low-latitude traveling ionospheric disturbances (TIDs). Three TID events were simultaneously observed by a 630.0-nm airglow imager and the CHAllenging Minisatellite Payload (CHAMP) satellite at Kototabang, Indonesia (geographic coordinates: 0.2 degrees S, 100.3 degrees E, geomagnetic latitude: 10.6 degrees S). In 630.0-nm airglow images of all three events, there are clear southward-moving structures. Events 1 and 2 are a single pulse with horizontal scales of similar to 500-1,000 km. Event 3 shows five wave fronts with a horizontal scale size of 500-1,000 km. All three TIDs are medium-scale TIDs. Horizontal wavelengths of both airglow intensity at an average emission altitude of 250 km and CHAMP neutral density variations measured at 400 km are estimated by fitting a sinusoidal function to the observed data. The estimated horizontal wavelengths for airglow and neutral density data are 1,031 and 880 km for event 1 and 560 and 420 km for event 3, respectively. These values between airglow and CHAMP are comparable, suggesting both instruments are observing the same wave. For event 1, the CHAMP electron density mapped along the geomagnetic field line onto the airglow altitude does not show wave structure similar to the airglow variation. For events 2 and 3, the plasma density did not show wavy structures similar to the waves seen in the airglow image and CHAMP neutral density. These results suggest that the TIDs observed in airglow images are not caused by ionospheric plasma instability but by gravity waves in the thermosphere.

    DOI: 10.1029/2018JA025634

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  64. Spatial Gradients in Geomagnetic Storm Time Currents Observed by Swarm Multispacecraft Mission Reviewed

    Vichare Geeta, Thomas Neethal, Shiokawa Kazau, Bhaskar Ankush, Sinha Ashwini Kumar

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 124 ( 2 ) page: 982 - 995   2019.2

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    This paper presents a comprehensive study of geomagnetic storm time currents using magnetic field recorded by multispacecraft polar-orbiting mission, Swarm. During geomagnetic storm period, the magnetic field variations obtained after removing the internal geomagnetic field and quiet time contributions can be considered as a proxy for storm time currents and are found to follow the temporal profile of Dst index very closely. These variations at the equatorial crossings recorded by multiple-spacecraft are used to estimate the Dst values and are found to have a good match with the ground-based Dst index. The average deviation between these two is around 4–13%. We have estimated the asymmetry by taking the difference between the magnetic field variations at two local time sectors separated by 12 hr. The estimated asymmetry shows a good match with the AsyH-index, especially when satellite traverses in the dawn-dusk sector. In general, the magnetic field variations are stronger in the night-to-dusk sector than day-to-dawn sector, which could be due to the larger pressure-gradients near night-to-dusk caused by ion movements. The important advantage of Swarm mission is that it provides an opportunity to investigate the longitudinal gradients in the storm time magnetic fields. It is observed that in general, the gradients are stronger during the main phase of the storm, centered near the equator with a latitudinal width of ~20–30° in both the hemispheres, and are supportive to the scenario of particle-injection from the magnetotail. The stronger gradients are observed at higher latitudes (~40°) during the episodes of substorms and might be associated with the ionospheric/field-aligned currents.

    DOI: 10.1029/2018JA025692

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  65. Visualization of rapid electron precipitation via chorus element wave-particle interactions Reviewed

    Mitsunori Ozaki, Yoshizumi Miyoshi, Kazuo Shiokawa, Keisuke Hosokawa, Shin-ichiro Oyama, Ryuho Kataoka, Yusuke Ebihara, Yasunobu Ogawa, Yoshiya Kasahara, Satoshi Yagitani, Yasumasa Kasaba, Atsushi Kumamoto, Fuminori Tsuchiya, Shoya Matsuda, Yuto Katoh, Mitsuru Hikishima, Satoshi Kurita, Yuichi Otsuka, Robert C. Moore, Yoshimasa Tanaka, Masahito Nose, Tsutomu Nagatsuma, Nozomu Nishitani, Akira Kadokura, Martin Connors, Takumi Inoue, Ayako Matsuoka, Iku Shinohara

    NATURE COMMUNICATIONS   Vol. 10 ( 1 ) page: 257   2019.1

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    Chorus waves, among the most intense electromagnetic emissions in the Earth's magnetosphere, magnetized planets, and laboratory plasmas, play an important role in the acceleration and loss of energetic electrons in the plasma universe through resonant interactions with electrons. However, the spatial evolution of the electron resonant interactions with electromagnetic waves remains poorly understood owing to imaging difficulties. Here we provide a compelling visualization of chorus element wave-particle interactions in the Earth's magnetosphere. Through in-situ measurements of chorus waveforms with the Arase satellite and transient auroral flashes from electron precipitation events as detected by 100-Hz video sampling from the ground, Earth's aurora becomes a display for the resonant interactions. Our observations capture an asymmetric spatial development, correlated strongly with the amplitude variation of discrete chorus elements. This finding is not theoretically predicted but helps in understanding the rapid scattering processes of energetic electrons near the Earth and other magnetized planets.

    DOI: 10.1038/s41467-018-07996-z

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  66. Transient ionization of the mesosphere during auroral breakup: Arase satellite and ground-based conjugate observations at Syowa Station Reviewed

    Ryuho Kataoka, Takanori Nishiyama, Yoshimasa Tanaka, Akira Kadokura, Herbert Akihito Uchida, Yusuke Ebihara, Mitsumu K. Ejiri, Yoshihiro Tomikawa, Masaki Tsutsumi, Kaoru Sato, Yoshizumi Miyoshi, Kazuo Shiokawa, Satoshi Kurita, Yoshiya Kasahara, Mitsunori Ozaki, Keisuke Hosokawa, Shoya Matsuda, Iku Shinohara, Takeshi Takashima, Tatsuhiko Sato, Takefumi Mitani, Tomoaki Hori, Nana Higashio

    EARTH PLANETS AND SPACE   Vol. 71 ( 1 ) page: 9   2019.1

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    Transient mesospheric echo in the VHF range was detected at an altitude of 65-70km during the auroral breakup that occurred from 2220 to 2226 UT on June 30, 2017. During this event, the footprint of the Arase satellite was located within the field of view of the all-sky imagers at Syowa Station in the Antarctic. Auroral observations at Syowa Station revealed the dominant precipitation of relatively soft electrons during the auroral breakup. A corresponding spike in cosmic noise absorption was also observed at Syowa Station, while the Arase satellite observed a flux enhancement of >100keV electrons and a broadband noise without detecting chorus waves or electromagnetic ion cyclotron waves. A general-purpose Monte Carlo particle transport simulation code was used to quantitatively evaluate the ionization in the middle atmosphere. Results of this study indicate that the precipitation of energetic electrons of >100keV, rather than X-rays from the auroral electrons, played a dominant role in the transient and deep (65-70km) mesospheric ionization during the observed auroral breakup.

    DOI: 10.1186/s40623-019-0989-7

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  67. PRELIMINARY RESULTS OF SIMULTANEOUS RECORDING OF AURORAL AND GEOMAGNETIC PULSATIONS AT THE ISTP SB RAS STATION ISTOK Reviewed

    Beletskii A. B., Rakhmatulin R. A., Syrenova T. Ye, Vasilev R. V., Mikhalev A. V, Pashinin A. Yu, Shiokawa K., Nishitani N.

    SOLAR-TERRESTRIAL PHYSICS   Vol. 5 ( 2 ) page: 39 - 44   2019

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    DOI: 10.12737/stp-52201906

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  68. Spatiotemporal development of pulsating auroral patch associated with discrete chorus elements: Arase and PWING observations

    Ozaki M, Shiokawa K, Miyoshi Y, Hosokawa K, Oyama S, Yagitani S, Kasahara Y, Kasaba Y, Matsuda S, Kataoka R, Ebihara Y, Ogawa Y, Otsuka Y, Kurita S, Moore R. C, Tanaka Y. -M, Nose M, Nagatsuma T, Connors M, Nishitani N, Hikishima M, Kumamoto A, Tsuchiya F, Kadokura A, Nishiyama T, Inoue T, Imamura K, Matsuoka A, Shinohara I

    2019 URSI ASIA-PACIFIC RADIO SCIENCE CONFERENCE (AP-RASC)     page: .   2019

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  69. Preliminary results of simultaneous recording of auroral and geomagnetic pulsations at the ISTP SB RAS station Istok Reviewed

    Beletskii A.B., Rakhmatulin R.A., Syrenova T.Y., Vasilev R.V., Mikhalev A.V., Pashinin A.Y., Shiokawa K., Nishitani N.

    Solnecno-Zemnaa Fizika   Vol. 5 ( 2 ) page: 43 - 48   2019

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    The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September–December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer. Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals. In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.

    DOI: 10.12737/szf-52201906

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  70. Electrostatic Electron Cyclotron Harmonic Waves as a Candidate to Cause Pulsating Auroras Reviewed

    M. Fukizawa, T. Sakanoi, Y. Miyoshi, K. Hosokawa, K. Shiokawa, Y. Katoh, Y. Kazama, A. Kumamoto, F. Tsuchiya, Y. Miyashita, Y. M. Tanaka, Y. Kasahara, M. Ozaki, A. Matsuoka, S. Matsuda, M. Hikishima, S. Oyama, Y. Ogawa, S. Kurita, R. Fujii

    Geophysical Research Letters   Vol. 45 ( 23 ) page: 12,661 - 12,668   2018.12

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    ©2018. American Geophysical Union. All Rights Reserved. Pulsating auroras (PsAs) are thought to be generated by precipitating electrons scattered by lower-band chorus (LBC) waves near the magnetic equator. One-to-one correlation between the LBC intensity and the PsA intensity has been reported. Electrostatic electron cyclotron harmonic (ECH) waves can also scatter electrons. However, direct correlation between ECH and PsA has not been reported yet. In this study, using a coordinated Exploration of energization and Radiation in Geospace (Arase) satellite and ground-based imager observation, we report that not only LBC but also ECH have correlation with PsA. We estimated the precipitating electron energy by assuming that the time lag when the cross-correlation coefficient became the highest was travel time of electrons from the modulation region. We found that the estimated energies show reasonable values as the cyclotron resonance energy of each wave.

    DOI: 10.1029/2018GL080145

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  71. Rapid Loss of Relativistic Electrons by EMIC Waves in the Outer Radiation Belt Observed by Arase, Van Allen Probes, and the PWING Ground Stations

    Kurita S, Miyoshi Y, Shiokawa K, Higashio N, Mitani T, Takashima T, Matsuoka A, Shinohara I, Kletzing C. A, Blake J. B, Claudepierre S. G, Connors M, Oyama S, Nagatsuma T, Sakaguchi K, Baishev D, Otsuka Y

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 23 ) page: 12720-12729 - 12,729   2018.12

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    DOI: 10.1029/2018GL080262

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  72. The ARASE (ERG) magnetic field investigation Reviewed

    Matsuoka A, Teramoto M, Nomura R, Nosé M, Fujimoto A, Tanaka Y, Shinohara M, Nagatsuma T, Shiokawa K, Obana Y, Miyoshi Y, Mita M, Takashima T, Shinohara I

    Earth, Planets and Space   Vol. 70 ( 1 )   2018.12

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    © 2018, The Author(s). The fluxgate magnetometer for the Arase (ERG) spacecraft mission was built to investigate particle acceleration processes in the inner magnetosphere. Precise measurements of the field intensity and direction are essential in studying the motion of particles, the properties of waves interacting with the particles, and magnetic field variations induced by electric currents. By observing temporal field variations, we will more deeply understand magnetohydrodynamic and electromagnetic ion-cyclotron waves in the ultra-low-frequency range, which can cause production and loss of relativistic electrons and ring-current particles. The hardware and software designs of the Magnetic Field Experiment (MGF) were optimized to meet the requirements for studying these phenomena. The MGF makes measurements at a sampling rate of 256 vectors/s, and the data are averaged onboard to fit the telemetry budget. The magnetometer switches the dynamic range between ± 8000 and ± 60,000 nT, depending on the local magnetic field intensity. The experiment is calibrated by preflight tests and through analysis of in-orbit data. MGF data are edited into files with a common data file form

    DOI: 10.1186/s40623-018-0800-1

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  73. Large-Scale Ducting of Pc1 Pulsations Observed by Swarm Satellites and Multiple Ground Networks Reviewed

    Hyangpyo Kim, Junga Hwang, Jaeheung Park, Yukinaga Miyashita, Kazuo Shiokawa, Ian R. Mann, Tero Raita, Jaejin Lee

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 23 ) page: 12703 - 12712   2018.12

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    Low Earth orbit satellites frequently encounter Pc1 pulsations, but most have been observed with limited latitudinal extent or short lifetime. In this study we analyze two large-scale Pc1 pulsations (both latitudinally wide and long-lasting) generated by ionospheric ducting effect using Swarm and ground magnetometers on 25 June and 3 September 2015. Swarm observed the 25 June pulsations on both dayside and nightside during the storm time substorm (a strong geomagnetic storm on 23 June with D-st = - 204 nT). We found the Pc1 pulsations were pervasive in both magnetic local time sectors of dayside and nightside for at least 2 hr. Another large Pc1 pulsation on 3 September was observed during a nonstorm substorm period. We conclude that (1) ionospheric ducting can transmit Pc1 waves to a wide range of L shells, (2) geomagnetic storm is not a prerequisite for such large-scale ducting, and (3) wave intensity can abruptly decrease across sharp gradients in the ionospheric plasma density.

    DOI: 10.1029/2018GL080693

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  74. Microscopic Observations of Pulsating Aurora Associated With Chorus Element Structures: Coordinated Arase Satellite-PWING Observations Reviewed

    Ozaki M, Shiokawa K, Miyoshi Y, Hosokawa K, Oyama S, Yagitani S, Kasahara Y, Kasaba Y, Matsuda S, Kataoka R, Ebihara Y, Ogawa Y, Otsuka Y, Kurita S, Moore R. C, Tanaka Y. -M, Nose M, Nagatsuma T, Connors M, Nishitani N, Katoh Y, Hikishima M, Kumamoto A, Tsuchiya F, Kadokura A, Nishiyama T, Inoue T, Imamura K, Matsuoka A, Shinohara I

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 22 ) page: 12125 - 12134   2018.11

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    DOI: 10.1029/2018GL079812

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  75. Statistical Analysis of SAR Arc Detachment From the Main Oval Based on 11-Year, AII-sky Imaging Observation at Athabasca, Canada Reviewed

    Yuki Takagi, Kazuo Shiokawa, Yuichi Otsuka, Martin Connors, Ian Schofield

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 21 ) page: 11539 - 11546   2018.11

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    We report the first statistical analysis of stable auroral red (SAR) arc detachments from the main auroral oval, using 630-nm all-sky cooled-Charge Coupled Device images obtained at Athabasca (magnetic latitude = 61.7 degrees N), Canada. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of ring current particle injection in the inner magnetosphere. We analyzed all-sky images obtained for 11 years from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur in the premidnight sector, indicating the ring current ion drift to the dusk sector. The SAR arc detachments also tend to occur at the beginning of the substorm recovery phase, suggesting that the SAR arcs detach from the main oval as the main auroral oval returns to higher latitudes. The equatorward velocities of detached SAR arcs are from -100 m/s (poleward) to +200 m/s (equatorward), corresponding to magnetospheric electric fields from -1 to +2 mV/m.Plain Language, Summary Stable auroral red (SAR) arcs are the optical emissions caused by low-energy electron precipitation into the ionosphere from the inner magnetosphere close to the earth. In this paper, we report the first statistical analysis of SAR arc detachments from the main auroral oval, using all-sky cooled-Charge Coupled Device images measured at a wavelength of 630.0 nm obtained at Athabasca, Canada, which is located at latitudes just lower than the auroral zone latitudes. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of high-energy particle injection in the inner magnetosphere. We analyzed 11-year all-sky images from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur premidnight, indicating the high-energy ion drift to the dusk sector. We also found that the SAR arc detachments tend to occur at the beginning of the substorm recovery phase. This likely indicates that the SAR arcs detach from the high-latitude aurora as the main aurora returns to higher latitudes at the beginning of the recovery phase. The equatorward velocities of detached SAR arcs are also estimated from the analysis.

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  76. Comparison of gravity wave propagation directions observed by mesospheric airglow imaging at three different latitudes using the M-transform Reviewed

    Septi Perwitasari, Takuji Nakamura, Masaru Kogure, Yoshihiro Tomikawa, Mitsumu K. Ejiri, Kazuo Shiokawa

    ANNALES GEOPHYSICAE   Vol. 36 ( 6 ) page: 1597 - 1605   2018.11

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    We developed user-friendly software based on Matsuda et al.'s (2014) 3D-FFT method (Matsuda-transform, M-transform) for airglow imaging data analysis as a function of Interactive Data Language (IDL). Users can customize the range of wave parameters to process when executing the program. The input for this function is a 3-D array of a time series of a 2-D airglow image in geographical coordinates. We applied this new function to mesospheric airglow imaging data with slightly different observation parameters obtained for the period of April-May at three different latitudes: Syowa Station, the Antarctic (69 degrees S, 40 degrees E); Shigaraki, Japan (35 degrees N, 136 degrees E); and Tomohon, Indonesia (1 degrees N, 122 degrees E). The day-to-day variation of the phase velocity spectrum at the Syowa Station is smaller and the propagation direction is mainly westward. In Shigaraki, the day-to-day variation of the horizontal propagation direction is larger than that at the Syowa Station; the variation in Tomohon is even larger. In Tomohon, the variation of the nightly power spectrum magnitude is remarkable, which indicates the intermittency of atmospheric gravity waves (AGWs). The average nightly spectrum obtained from April-May shows that the dominant propagation is westward with a phase speed < 50 m s(-1) at the Syowa Station and east-southeastward with a phase speed of up to similar to 80 m s(-1) in Shigaraki. The day-to-day variation in Tomohon is too strong to discuss average characteristics; however, a phase speed of up to similar to 100 m s(-1) and faster is observed. The corresponding background wind profiles derived from MERRA-2 indicate that wind filtering plays a significant role in filtering out waves that propagate eastward at the Syowa Station. On the other hand, the background wind is not strong enough to filter out relatively high-speed AGWs in Shigaraki and Tomohon and the dominant propagation direction is likely related to the distribution and characteristics of the source region, at least in April and May.

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  77. Variability of the Sun and Its Terrestrial Impacts Reviewed

    Katya Georgieva, Kazuo Shiokawa

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 180   page: 1 - 2   2018.11

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    DOI: 10.1016/j.jastp.2018.09.008

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  78. Energetic electron precipitation associated with pulsating aurora observed by VLF radio propagation during recovery phase of substorm on 27 March 2017 Reviewed

    Tsuchiya,F, A. Hirai, T. Obara, H. Misawa, S. Kurita, Y. Miyoshi, K. Shiokawa, M. Connors, M. Ozaki, Y. Kasahara, A. Kumamoto, Y. Kasaba, A. Matsuoka, M. Shoji, I. Shinohara

    Geophysical Research Letters   Vol. 45 ( 23 ) page: 12,651 - 12,660   2018.11

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    DOI: 10.1029/2018GL080222

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  79. サブオーロラ帯におけるEMIC波動と高エネルギー電子降下観測

    平井あすか, 土屋史紀, 小原隆博, 笠羽康正, 加藤雄人, 三澤浩昭, 塩川和夫, 三好由純, 栗田怜, Martin Connors

    宇宙航空研究開発機構特別資料: 第15回「宇宙環境シンポジウム」講演論文集     page: 11 - 16   2018.11

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    放射線帯外帯の相対論的電子は、磁気圏内で発生するプラズマ波動との相互作用により散乱され地球大気に降下する。この過程は、磁気嵐の主相における外帯消失の要因の一つと考えられており、降下した相対論的電子は、国際宇宙ステーションや低軌道衛星への悪影響、下部電離圏での電子密度増加に伴う通信障害を引き起こし得る。本研究では、放射線帯の相対論的電子を降下消失させる電磁イオンサイクロトロン(EMIC)波動に着目した。電子降下は、VLF/LF帯の人工電波を用いて観測した。地上と電離圏下端の間を長距離伝搬する電波の信号は、電子降下に伴う電離圏D領域高度での局所的な擾乱により振幅・位相変調をうける。本研究では、複合地上観測により、2017年3月27日の磁気嵐主相時のEMIC波動とそれに伴う相対論的電子降下の時空間対応を調べた。その結果、数10秒から数分の時間スケールで変化するEMIC波動強度の増大時に、相対論的電子が散乱され大気に降下消失することが明らかとなった。

  80. Temporal and Spatial Correspondence of Pc1/EMIC Waves and Relativistic Electron Precipitations Observed with Ground-Based Multi-Instruments on 27 March 2017 Reviewed

    Hirai, A, F. Tsuchiya, T. Obara, Y. Kasaba, Y. Katoh, H. Misawa, K. Shiokawa, Y. Miyoshi, S. Kurita, S. Matsuda, M. Connors, T. Nagatsuma, K. Sakaguchi, Y. Kasahara, A. Kumamoto, A. Matsuoka, M. Shoji, I. Shinohara, J. M. Albert

    Geophysical Research Letters   Vol. 45 ( 24 ) page: 13,182 - 13,191   2018.11

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    DOI: 10.1029/2018GL080126

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  81. Statistical Study of Phase Relationship Between Magnetic and Plasma Pressures in the Near-Earth Nightside Magnetosphere Using the THEMIS-E Satellite Reviewed

    Katsuki Nishi, Kazuo Shiokawa, Karl-Heinz Glassmeier, Johannes Z. D. Mieth

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 11 ) page: 9517 - 9531   2018.11

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    Distributions of plasma and magnetic pressures are the basic information to investigate macroscopic dynamics of the Earth's magnetosphere. Several studies have been made on magnetic and plasma pressures and macroscopic plasma instabilities in the magnetosphere. However, correlation between magnetic and plasma pressure variations has not been statistically investigated. In this paper, we analyze the statistical characteristics of the phase relationships between variations of magnetic and plasma pressures at frequencies of 4-15 mHz using 2 years of the THEMIS-E satellite data in the nightside magnetosphere. Spectral peaks with coherence greater than 0.85 between magnetic and plasma pressures for 1-hr time segments were selected. The average occurrence rates of the phase relationships are antiphase (within +/- 10 degrees from 180 degrees), 39.75%; in-phase (within +/- 10 degrees from 0 degrees), 0.73%; and other phases (10-170 degrees), 49.83%. For the other-phase events, the phase differences are much closer to antiphase rather than to in-phase. Thus, we conclude that the two pressure variations tend to be antiphase. The antiphase and in-phase relationships are observed mainly at radial distances outside 8 R-E and inside 8 R-E, respectively. The high occurrence region of antiphase relationship is in the dawnside during magnetically quiet times and shifts to dusk side at active times defined as Dst < -10 nT. The occurrence rates of the phase relationships do not change significantly depending on the AE and Dst indices, plasma beta, and IMF-B-z. Based on these results, we discuss the correspondence between the phase relationships and the possible magnetohydrodynamic force balances that can produce these phase relationships.

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  82. Purple Auroral Rays and Global Pc1 Pulsations Observed at the CIR-Associated Solar Wind Density Enhancement on 21 March 2017 Reviewed

    K. Shiokawa, M. Ozaki, A. Kadokura, Y. Endo, T. Sakanoi, S. Kurita, Y. Miyoshi, S. I. Oyama, M. Connors, I. Schofield, J. M. Ruohoniemi, M. Nośe, T. Nagatsuma, K. Sakaguchi, D. G. Baishev, A. Pashinin, R. Rakhmatulin, B. Shevtsov, I. Poddelsky, M. Engebretson, Tero Raita, Y. M. Tanaka, M. Shinohara, M. Teramoto, R. Nomura, A. Fujimoto, A. Matsuoka, N. Higashio, T. Takashima, I. Shinohara, Jay M. Albert

    Geophysical Research Letters   Vol. 45 ( 20 ) page: 10,819 - 10,828   2018.10

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    ©2018. American Geophysical Union. All Rights Reserved. This paper reports two unique auroral features: postmidnight purple auroral rays and global Pc1 geomagnetic pulsations, observed before the onset of the corotating interaction region (CIR) storm of 21 March 2017, at the beginning of the first campaign of the new Particles and Waves in the Inner magnetosphere using Ground-based network observation (PWING) longitudinal ground network with the Arase satellite. The purple auroral rays were observed from ~0315 to 0430 UT (~03–04 magnetic local time) in the northeastern sky at Husafell, Iceland (magnetic latitude: 64.9°N). We newly propose that the entry of high-density CIR plasma into the magnetotail created purple auroral rays in the sunlit ionosphere. Pc1 geomagnetic pulsations at frequencies of 0–0.5 Hz were observed after ~00 UT over a wide local time range, of 13 hr, from midnight to afternoon sectors at subauroral latitudes associated with CIR arrival. These results indicate preconditioning of the magnetosphere due to crossing of a CIR.

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  83. Global Distribution of ULF Waves During Magnetic Storms: Comparison of Arase, Ground Observations, and BATSRUSC plus CRCM Simulation Reviewed

    Naoko Takahashi, Kanako Seki, Mariko Teramoto, Mei-Ching Fok, Yihua Zheng, Ayako Matsuoka, Nana Higashio, Kazuo Shiokawa, Dmitry Baishev, Akimasa Yoshikawa, Tsutomu Nagatsuma

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 18 ) page: 9390 - 9397   2018.9

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    During 26-29 March 2017 magnetic storm, the Arase satellite observed typical ultra low frequency (ULF) waves and acceleration of relativistic electrons. We simulate the global distribution of these ULF waves using CRCM with BATSRUS global magnetospheric magnetohydrodynamic model. The simulation can qualitatively reproduce the ULF waves observed by Arase at frequencies of 2-3 mHz. However, the simulated ULF wave power is 1-2 orders of magnitude smaller than the observation. The simulated ULF wave activity has a good correlation with the solar-wind dynamic pressure variation, while the wave activity on the ground is enhanced even during the recovery phase, possibly due to the Kelvin-Helmholtz instability and/or substorms. We also study the 3-6 April 2017 magnetic storm, in which low ULF wave activity and weak acceleration of relativistic electrons are seen. We suggest that the existence of ULF waves plays an important role in accelerating electrons up to relativistic energies.Plain Language Summary The Earth has the region of space that is controlled by the Earth's magnetic field, called the magnetosphere. When the temporary disturbance of the magnetosphere (magnetic storm) occurs, extremely high-energy electrons (a few MeV) accelerate around the Earth. It is considered that periodic waves with a frequency of 1-20 mHz, known as ultra low frequency (ULF) waves, play an important role in accelerating electrons up to relativistic energies. On 27 March 2017, Japanese satellite, called as "Arase," successfully observed ULF waves. We focus on this ULF waves and investigate the global activity of ULF waves using both numerical simulations and observations. The numerical simulation using in this study qualitatively reproduced the enhancement of ULF waves with a frequency range of 1.6-6.7 mHz, but its intensity is smaller than the Arase satellite observation. Comparing to ground observations, we found that the global ULF wave activity estimated by the numerical simulation is strongly affected by the dynamic pressure enhancement caused by a stream of charged particles from the Sun. In addition, we suggest that the ULF wave activity might affect the acceleration characteristics of high-energy electrons around the Earth.

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  84. Magnetospheric Source Region of Auroral Finger-like Structures Observed by the RBSP-A Satellite Reviewed

    Katsuki Nishi, Kazuo Shiokawa, Harlan Spence

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 9 ) page: 7513 - 7522   2018.9

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    Auroral finger-like structures appear equatorward of the auroral oval in the diffuse auroral region and contribute to the auroral fragmentation into patches. A previous report of the first conjugate observation of auroral finger-like structures using a Time History of Events and Macroscale Interactions during Substorms (THEMIS) Ground-Based Observatories camera and the THEMIS-E satellite at a radial distance of similar to 8 R-E showed antiphase oscillations of magnetic and plasma pressures in the dawnside plasma sheet. In the present study, we report another simultaneous observation of auroral finger-like structures at Gillam, Canada, at similar to 0900UT (0230 magnetic local time) on 14 November 2014 with the Radiation Belt Storm Probes satellites at 5.8R(E) in the inner magnetosphere. From this simultaneous observation event, we obtained the following observations. (1) Auroral finger-like structures developed poleward in the equatorward moving auroral arc at the equatorward edge of the auroral oval. (2) Both the electron and ion OMNI fluxes measured by HOPE increased at approximate to 0900UT as the satellite footprint entered the auroral region, indicating that the satellite was crossing the observed auroral finger-like structures. (3) The absolute value of magnetic pressure was several times that of the plasma pressure, and no systematic phase relationship was identified between the magnetic and plasma pressures, unlike that in the THEMIS case. Based on these observations, we discuss two possible causes of the observed finger-like structures, namely, pressure-driven instability in the magnetosphere and gradient drift instability in the ionosphere. In this paper, the latter possibility is newly suggested to develop in the equatorward moving aurora associated with the westward electric field in the equatorward ionospheric density gradient.Plain Language Summary We report the conjugate observation of auroral finger-like structures using ground-based all-sky imager and the RBSP-A satellite. Such a report of conjugate observation of auroral finger-like structures with the RBSP-A satellite in the inner magnetosphere is for the first time. The auroral finger-like structures can be a cause of the auroral fragmentation into patches. From the present observation, we suggest that the gradient drift instability in the ionospheric plasma can be a cause of the auroral finger-like structures.

    DOI: 10.1029/2018JA025480

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  85. Investigation of Nighttime MSTIDS Observed by Optical Thermosphere Imagers at Low Latitudes: Morphology, Propagation Direction, and Wind Filtering Reviewed

    Figueiredo C, A. O. B, Takahashi H, Wrasse C. M, Otsuka Y, Shiokawa K, Barros D

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 9 ) page: 7843 - 7857   2018.9

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    DOI: 10.1029/2018JA025438

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  86. Statistical Analysis of the Phase Velocity Distribution of Mesospheric and Ionospheric Waves Observed in Airglow Images Over a 16-Year Period: Comparison Between Rikubetsu and Shigaraki, Japan Reviewed

    Tsuchiya Satoshi, Shiokawa Kazuo, Fujinami Hatsuki, Otsuka Yuichi, Nakamura Takuji, Yamamoto Mamoru

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 8 ) page: 6930-6947   2018.8

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    DOI: 10.1029/2018JA025585

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  87. EMIC Wave Events During the Four GEM QARBM Challenge Intervals Reviewed

    Engebretson M. J, Posch J. L, Braun D. J, Li W, Ma Q, Kellerman A. C, Huang C. -L, Kanekal S. G, Kletzing C. A, Wygant J. R, Spence H. E, Baker D. N, Fennell J. F, Angelopoulos V, Singer H. J, Lessard M. R, Horne R. B, Raita T, Shiokawa K, Rakhmatulin R, Dmitriev E, Ermakova E

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 8 ) page: 6394 - 6423   2018.8

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    DOI: 10.1029/2018JA025505

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  88. On the Role of Thermospheric Winds and Sporadic E Layers in the Formation and Evolution of Electrified MSTIDs in Geomagnetic Conjugate Regions Reviewed

    Narayanan V. L, Shiokawa K, Otsuka Y, Neudegg D

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 8 ) page: 6957 - 6980   2018.8

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    DOI: 10.1029/2018JA025261

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  89. Equatorial plasma bubble seeding by MSTIDs in the ionosphere Reviewed

    Takahashi Hisao, Wrasse Cristiano Max, Oliveira Barros Figueiredo Cosme Alexandre, Barros Diego, Abdu Mangalathayil Ali, Otsuka Yuichi, Shiokawa Kazuo

    PROGRESS IN EARTH AND PLANETARY SCIENCE   Vol. 5   2018.6

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    DOI: 10.1186/s40645-018-0189-2

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  90. Periodic Oscillations in the D Region Ionosphere After the 2011 Tohoku Earthquake Using LF Standard Radio Waves Reviewed

    Hiroyo Ohya, Fuminori Tsuchiya, Yuta Takishita, Hiroyuki Shinagawa, Kenro Nozaki, Kazuo Shiokawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 6 ) page: 5261 - 5270   2018.6

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    We report the first observations of similar to 100-s periodic oscillations of intensity in low-frequency (LF) standard radio waves over Japan at 05:51-05:56 UT, which was about 4min and 42s after mainshock onset of the 2011 off the Pacific coast of Tohoku earthquake on 11 March 2011 (Mw 9.0). The LF radio wave propagation paths used in this study were JJY (Japan, 60kHz)-Rikubetsu (RKB, Japan), and BPC (China, 68.5 kHz)-RKB, where the minimum distances between the epicenter and the LF propagation paths were 413.6 and 561.5 km, respectively. The observed modulations in intensity and phase were about 0.1 dB and 0.5 degrees, respectively. Based on a numerical simulation of the neutral atmosphere and the wave-hop method, the occurrence time of the similar to 100-s periodic oscillations was in good agreement with the total propagation time of the Rayleigh wave that spread concentrically from the epicenter to the LF propagation paths and acoustic waves propagating vertically from the Earth's surface to the bottom of the ionosphere. Variations in synthesized electric field intensity of ground waves and sky waves, calculated by the wave hop method up to 10 hops, reproduced similar similar to 100-s periodic oscillations that were caused by the difference in arrival time of the acoustic waves excited by the Rayleigh waves at each hop point. The amplitude of the D region electron density variations at 70km altitude during the similar to 100-s periodic oscillation was estimated to be about 1% compared to the background electron density, based on the numerical simulation.

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  91. Geospace exploration project ERG Reviewed

    Yoshizumi Miyoshi, Iku Shinohara, Takeshi Takashima, Kazushi Asamura, Nana Higashio, Takefumi Mitani, Satoshi Kasahara, Shoichiro Yokota, Yoichi Kazama, Shiang-Yu Wang, Sunny W. Y. Tam, Paul T. P. Ho, Yoshiya Kasahara, Yasumasa Kasaba, Satoshi Yagitani, Ayako Matsuoka, Hirotsugu Kojima, Yuto Katoh, Kazuo Shiokawa, Kanako Seki

    EARTH PLANETS AND SPACE   Vol. 70 ( 1 )   2018.6

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    The Exploration of energization and Radiation in Geospace (ERG) project explores the acceleration, transport, and loss of relativistic electrons in the radiation belts and the dynamics for geospace storms. This project consists of three research teams for satellite observation, ground-based network observation, and integrated data analysis/simulation. This synergetic approach is essential for obtaining a comprehensive understanding of the relativistic electron generation/loss processes of the radiation belts as well as geospace storms through cross-energy/cross-regional couplings, in which different plasma/particle populations and regions are strongly coupled with each other. This paper gives an overview of the ERG project and presents the initial results from the ERG (Arase) satellite.

    DOI: 10.1186/s40623-018-0862-0

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  92. The ARASE (ERG) magnetic field investigation Reviewed

    能勢 正仁, Teramoto Mariko, Nomura Reiko, Nosé Masahito, Fujimoto Akiko, Tanaka Yoshimasa, Shinohara Manabu, Nagatsuma Tsutomu, Shiokawa Kazuo, Obana Yuki, Miyoshi Yoshizumi, Mita Makoto, Takashima Takeshi, Shinohara Iku

    Earth, Planets and Space   ( 70 )   2018.3

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    The fluxgate magnetometer for the Arase (ERG) spacecraft mission was built to investigate particle acceleration processes in the inner magnetosphere. Precise measurements of the field intensity and direction are essential in studying the motion of particles, the properties of waves interacting with the particles, and magnetic field variations induced by electric currents. By observing temporal field variations, we will more deeply understand magnetohydrodynamic and electromagnetic ion-cyclotron waves in the ultra-low-frequency range, which can cause production and loss of relativistic electrons and ring-current particles. The hardware and software designs of the Magnetic Field Experiment (MGF) were optimized to meet the requirements for studying these phenomena. The MGF makes measurements at a sampling rate of 256 vectors/s, and the data are averaged onboard to fit the telemetry budget. The magnetometer switches the dynamic range between ± 8000 and ± 60, 000 nT, depending on the local magnetic field intensity. The experiment is calibrated by preflight tests and through analysis of in-orbit data. MGF data are edited into files with a common data file format, archived on a data server, and made available to the science community. Magnetic field observation by the MGF will significantly improve our knowledge of the growth and decay of radiation belts and ring currents, as well as the dynamics of geospace storms.

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  93. Medium-Scale Traveling Ionospheric Disturbances Observed by Detrended Total Electron Content Maps Over Brazil Reviewed

    Figueiredo C. A. O. B., Takahashi H., Wrasse C. M., Otsuka Y., Shiokawa K., Barros D.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 123 ( 3 ) page: 2215-2227   2018.3

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    DOI: 10.1002/2017JA025021

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  94. Discovery of 1Hz Range Modulation of Isolated Proton Aurora at Subauroral Latitudes Reviewed

    海老原 祐輔, Shiokawa K., Miyoshi Y., Kataoka R., Connors M., Inoue T., Yagitani S., Ebihara Y., Jun C.-W., Nomura R., Sakaguchi K., Otsuka Y., Uchida H. A., Schofield I., Danskin D. W.

    Geophysical Research Letters   Vol. 45 ( 3 ) page: 1209 - 1217   2018.2

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    Isolated proton aurora (IPA) is a manifestation of the wave‐particle interaction visible at subauroral latitudes, with activity on many timescales. We herein present the first observational evidence of rapid luminous modulation of IPA correlated with simultaneously observed Pc1 waves observed on the ground, which are equivalent to the electromagnetic ion cyclotron (EMIC) waves in the magnetosphere. The fastest luminous modulation of IPA was observed in the 1 Hz frequency range, which was twice the frequency of the related Pc1 waves. The time lag between variations of Pc1 wave power and the IPA luminosity suggests that the source regions of IPA are distributed near the magnetic equator, suggesting an EMIC wave‐energetic (a few tens of keV) proton or relativistic (MeV or sub‐MeV) electron interaction. The generation mechanism of this 1 Hz luminous modulation remains an open issue, but this study supports the importance of nonlinear pitch angle scattering via wave‐particle interactions.

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  95. Discovery of 1Hz Range Modulation of Isolated Proton Aurora at Subauroral Latitudes

    Ozaki M., Shiokawa K., Miyoshi Y., Kataoka R., Connors M., Inoue T., Yagitani S., Ebihara Y., Jun C. -W., Nomura R., Sakaguchi K., Otsuka Y., Uchida H. A., Schofield I., Danskin D. W.

    GEOPHYSICAL RESEARCH LETTERS   Vol. 45 ( 3 ) page: 1209-1217   2018.2

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    DOI: 10.1002/2017GL076486

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  96. Observations of aurora and electromagnetic disturbances originated from dynamic plasma variations in the Earth's inner magnetosphere Reviewed

    Shiokawa Kazuo

    Meeting Abstracts of the Physical Society of Japan   Vol. 73 ( 0 ) page: 766 - 766   2018

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    DOI: 10.11316/jpsgaiyo.73.1.0_766

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  97. First Study on the Occurrence Frequency of Equatorial Plasma Bubbles over West Africa Using an All-Sky Airglow Imager and GNSS Receivers

    Okoh Daniel, Rabiu Babatunde, Shiokawa Kazuo, Otsuka Yuichi, Segun Bolaji, Falayi Elijah, Onwuneme Sylvester, Kaka Rafiat

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 12 ) page: 12430-12444   2017.12

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    DOI: 10.1002/2017JA024602

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  98. Ground-based instruments of the PWING project to investigate dynamics of the inner magnetosphere at subauroral latitudes as a part of the ERG-ground coordinated observation network

    Shiokawa Kazuo, Katoh Yasuo, Hamaguchi Yoshiyuki, Yamamoto Yuka, Adachi Takumi, Ozaki Mitsunori, Oyama Shin-Ichiro, Nose Masahito, Nagatsuma Tsutomu, Tanaka Yoshimasa, Otsuka Yuichi, Miyoshi Yoshizumi, Kataoka Ryuho, Takagi Yuki, Takeshita Yuhei, Shinbori Atsuki, Kurita Satoshi, Hori Tomoaki, Nishitani Nozomu, Shinohara Iku, Tsuchiya Fuminori, Obana Yuki, Suzuki Shin, Takahashi Naoko, Seki Kanako, Kadokura Akira, Hosokawa Keisuke, Ogawa Yasunobu, Connors Martin, Ruohoniemi J. Michael, Engebretson Mark, Turunen Esa, Ulich Thomas, Manninen Jyrki, Raita Tero, Kero Antti, Oksanen Arto, Back Marko, Kauristie Kirsti, Mattanen Jyrki, Baishev Dmitry, Kurkin Vladimir, Oinats Alexey, Pashinin Alexander, Vasilyev Roman, Rakhmatulin Ravil, Bristow William, Karjala Marty

    EARTH PLANETS AND SPACE   Vol. 69   2017.11

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    DOI: 10.1186/s40623-017-0745-9

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  99. Special Issue "Global data systems for the study of solar-terrestrial variability"

    Watanabe Takashi, Iyemori Toshihiko, Shiokawa Kazuo, Zhang Jie, Kanekal Shrikanth G., Nishitani Nozomu

    EARTH PLANETS AND SPACE   Vol. 69   2017.11

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    DOI: 10.1186/s40623-017-0742-z

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  100. Geomagnetically conjugate observations of ionospheric and thermospheric variations accompanied by a midnight brightness wave at low latitudes (vol 69, 112, 2017) Reviewed

    D. Fukushima, K. Shiokawa, Y. Otsuka, M. Kubota, T. Yokoyama, M. Nishioka, S. Komonjinda, C. Y. Yatini

    EARTH PLANETS AND SPACE   Vol. 69   2017.11

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    DOI: 10.1186/s40623-017-0729-9

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  101. GPS amplitude and phase scintillation associated with polar cap auroral forms

    Jayachandran P. T., Hamza A. M., Hosokawa K., Mezaoui H., Shiokawa K.

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 164   page: 185-191   2017.11

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    DOI: 10.1016/j.jastp.2017.08.030

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  102. Statistical analysis of severe magnetic fluctuations in the near-Earth plasma sheet observed by THEMIS-E

    Xu Heqiucen, Shiokawa Kazuo, Fruehauff Dennis

    ANNALES GEOPHYSICAE   Vol. 35 ( 5 ) page: 1131-1142   2017.10

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    DOI: 10.5194/angeo-35-1131-2017

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  103. Geomagnetically conjugate observations of ionospheric and thermospheric variations accompanied by a midnight brightness wave at low latitudes

    Fukushima D., Shiokawa K., Otsuka Y., Kubota M., Yokoyama T., Nishioka M., Komonjinda S., Yatini C. Y.

    EARTH PLANETS AND SPACE   Vol. 69   2017.8

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    DOI: 10.1186/s40623-017-0698-z

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  104. Equinoctial asymmetry in the zonal distribution of scintillation as observed by GPS receivers in Indonesia

    Abadi P., Otsuka Y., Shiokawa K., Husin A., Liu Huixin, Saito S.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 8 ) page: 8947-8958   2017.8

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    DOI: 10.1002/2017JA024146

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  105. Sixteen year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki, Japan

    Takeo D., Shiokawa K., Fujinami H., Otsuka Y., Matsuda T. S., Ejiri M. K., Nakamura T., Yamamoto M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 8 ) page: 8770-8780   2017.8

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    DOI: 10.1002/2017JA023919

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  106. Sixteen-year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki Reviewed

    Takeo, D, K. Shiokawa, H. Fujinami, Y. Otsuka, T. S. Matsuda, M. K. Ejiri, T. Nakamura, M. Yamamoto

    Journal of Geophysical Research -Atmospheres   Vol. 122   page: 8770-8780   2017.8

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    DOI: 10.0002/2017JA023919

  107. Conjugate observation of auroral finger-like structures by ground-based all-sky cameras and THEMIS satellites

    Nishi Katsuki, Shiokawa Kazuo, Fruehauff Dennis

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 7 ) page: 7291-7306   2017.7

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    DOI: 10.1002/2016JA023774

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  108. Coordinated observations of postmidnight irregularities and thermospheric neutral winds and temperatures at low latitudes

    Dao Tam, Otsuka Yuichi, Shiokawa Kazuo, Nishioka Michi, Yamamoto Mamoru, Buhari Suhaila M., Abdullah Mardina, Husin Asnawi

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 7 ) page: 7504-7518   2017.7

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    DOI: 10.1002/2017JA024048

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  109. Geospace exploration project: Arase (ERG)

    E. R.G, Project Group, Y. Miyoshi, Y. Kasaba, I. Shinohara, T. Takashima, K. Asamura, H. Matsumoto, N. Higashio, T. Mitani, S. Kasahara, S. Yokota, S. Wang, Y. Kazama, Y. Kasahara, S. Yagitani, A. Matsuoka, H. Kojima, Y. Katoh, K. Shiokawa, K. Seki, M. Fujimoto, T. Ono

    Journal of Physics: Conference Series   Vol. 869 ( 1 )   2017.7

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    © Published under licence by IOP Publishing Ltd. The ERG (Exploration of energization and Radiation in Geospace) is Japanese geospace exploration project. The project focuses on relativistic electron acceleration mechanism of the outer belt and dynamics of space storms in the context of the cross-energy coupling via wave-particle interactions. The project consists of the satellite observation team, the ground-based network observation team, and integrated-data analysis/simulation team. The satellite was launched on December 20 2016 and has been nicknamed, &quot;Arase&quot;. This paper describes overview of the project and future plan for observations.

    DOI: 10.1088/1742-6596/869/1/012095

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  110. Electron density variability of nighttime D region ionosphere in Vietnamese and Japanese sectors

    Le Minh Tan, Shiokawa Kazuo, Nguyen Ngoc Thu, Tran Quoc Ha

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 6 ) page: 6543-6551   2017.6

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    DOI: 10.1002/2017JA024025

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  111. Simultaneous observations of magnetospheric ELF/VLF emissions in Canada, Finland, and Antarctica

    Yonezu Yusuke, Shiokawa Kazuo, Connors Martin, Ozaki Mitsunori, Manninen Jyrki, Yamagishi Hisao, Okada Masaki

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 6 ) page: 6442-6454   2017.6

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    DOI: 10.1002/2017JA024211

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  112. First evidence of patchy flickering aurora modulated by multi-ion electromagnetic ion cyclotron waves

    Fukuda Yoko, Kataoka Ryuho, Uchida Herbert Akihito, Miyoshi Yoshizumi, Hampton Donald, Shiokawa Kazuo, Ebihara Yusuke, Whiter Daniel, Iwagami Naomoto, Seki Kanako

    GEOPHYSICAL RESEARCH LETTERS   Vol. 44 ( 9 ) page: 3963-3970   2017.5

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    DOI: 10.1002/2017GL072956

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  113. Contribution of storm time substorms to the prompt electric field disturbances in the equatorial ionosphere

    Hui Debrup, Chakrabarty D., Sekar R., Reeves G. D., Yoshikawa A., Shiokawa K.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 5 ) page: 5568-5578   2017.5

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    DOI: 10.1002/2016JA023754

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  114. Effect of the Ionospheric Parameter Variations at Altitudes of 80-350 km on Diurnal Dynamics of the ULF Magnetic Field Spectra at Midlatitudes

    Ermakova E. N., Kotik D. S., Pershin A. V., Pilipenko V. A., Shiokawa K.

    RADIOPHYSICS AND QUANTUM ELECTRONICS   Vol. 59 ( 12 ) page: 947-961   2017.5

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    DOI: 10.1007/s11141-017-9764-4

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  115. Automatic selection of Dst storms and their seasonal variations in two versions of Dst in 50 years

    Balan N., Tulasiram S., Kamide Y., Batista I. S., Souza J. R., Shiokawa K., Rajesh P. K., Victor N. J.

    EARTH PLANETS AND SPACE   Vol. 69   2017.4

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    DOI: 10.1186/s40623-017-0642-2

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  116. Measurement of thermospheric temperatures using OMTI Fabry-Perot interferometers with 70-mm etalon

    Nakamura Y., Shiokawa K., Otsuka Y., Oyama S., Nozawa S., Komolmis T., Komonjida S., Neudegg Dave, Yuile Colin, Meriwether J., Shinagawa H., Jin H.

    EARTH PLANETS AND SPACE   Vol. 69   2017.4

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    DOI: 10.1186/s40623-017-0643-1

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  117. Large-scale traveling ionospheric disturbances observed by GPS dTEC maps over North and South America on Saint Patrick's Day storm in 2015

    Figueiredo C. A. O. B., Wrasse C. M., Takahashi H., Otsuka Y., Shiokawa K., Barros D.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 4 ) page: 4755-4763   2017.4

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    DOI: 10.1002/2016JA023417

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  118. A scheme for forecasting severe space weather

    Balan N., Ebihara Y., Skoug R., Shiokawa K., Batista I. S., Ram S. Tulasi, Omura Y., Nakamura T., Fok M. -C.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 122 ( 3 ) page: 2824-2835   2017.3

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    DOI: 10.1002/2016JA023853

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  119. Localized polar cap precipitation in association with nonstorm time airglow patches

    Zou Ying, Nishimura Yukitoshi, Lyons Larry R., Shiokawa Kazuo

    GEOPHYSICAL RESEARCH LETTERS   Vol. 44 ( 2 ) page: 609-617   2017.1

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    DOI: 10.1002/2016GL071168

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  120. On the effect of thermospheric neutral winds on post-midnight field-aligned irregularities at low latitudes Reviewed

    Tam Dao, Yuichi Otsuka, Kazuo Shiokawa, Michi Nishioka, Mamoru Yamamoto, Suhaila M. Buhari, Mardina Abdullah, Asnawi Husin

    2017 XXXIIND GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM OF THE INTERNATIONAL UNION OF RADIO SCIENCE (URSI GASS)   Vol. 2017-January   page: 1 - 4   2017

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    We investigated a post-midnight Field-Aligned Irregularities (FAIs) event observed with the Equatorial Atmosphere Radar (EAR) at Kototabang (0.2 degrees S, 100.3 degrees E, dip lat. 10.4 degrees S) in Indonesia on the night of 9 July 2010, using a comprehensive dataset of both neutral and plasma parameters. We compared FAI echoes collocated with 630 nm airglow depletion detected by an all-sky imager. The thermospheric neutral winds and temperatures obtained by a Fabry-Perot interferometer at Kototabang and the altitudes of F-layer (h'F) observed with ionosondes at Kototabang, Chiang Mai, and Chumphon were also examined. We found that the 3-m scale post-midnight FAIs occurred within plasma bubbles. The convergence of the equatorward neutral winds happened in this particular event related to midnight temperature maximum (MTM) and that the equatorward winds in both northern and southern hemispheres could be responsible for the growth of plasma bubbles around midnight. The uplift of F-layer at low latitudes could increase the growth rate of the Rayleigh-Taylor instability. Eastward electric currents driven by the equatorward winds could also contribute to the generation of the irregularities at post-midnight.

    DOI: 10.23919/URSIGASS.2017.8105106

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    Other Link: http://orcid.org/0000-0002-4957-764X

  121. The first long-term all-sky imager observation of lunar sodium tail Reviewed

    Nishino Masaki N., Shiokawa Kazuo, Otsuka Yuichi

    ICARUS   Vol. 280   page: 199-204   2016.12

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    DOI: 10.1016/j.icarus.2016.08.004

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  122. Ionospheric TEC Weather Map Over South America Reviewed

    H. Takahashi, C. M. Wrasse, C. M. Denardini, M. B. Padua, E. R. de Paula, S. M. A. Costa, Y. Otsuka, K. Shiokawa, J. F. Galera Monico, A. Ivo, N. Sant'Anna

    SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS   Vol. 14 ( 11 ) page: 937 - 949   2016.11

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    Ionospheric weather maps using the total electron content (TEC) monitored by ground-based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Continuo) RBMC/Brazilian Institute for Geography and Statistics, Low-latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total similar to 140 sites, have been used. TECMAPs with a time resolution of 10min are produced in 12h time delay. Spatial resolution of the map is rather low, varying between 50 and 500km depending on the density of the observation points. Large day-to-day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1TECU=10(16)elm(-2) (TECU) &lt;10) to the crest region (TECU&gt;80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS-based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high-technology positioning system and telecommunication.

    DOI: 10.1002/2016SW001474

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  123. Localized field-aligned currents in the polar cap associated with airglow patches Reviewed

    Zou Ying, Nishimura Yukitoshi, Burchill Johnathan K., Knudsen David J., Lyons Larry R., Shiokawa Kazuo, Buchert Stephan, Chen Steve, Nicolls Michael J., Ruohoniemi J. Michael, McWilliams Kathryn A., Nishitani Nozomu

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 10 ) page: 10172-10189   2016.10

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    DOI: 10.1002/2016JA022665

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  124. Heliospheric plasma sheet (HPS) impingement onto the magnetosphere as a cause of relativistic electron dropouts (REDs) via coherent EMIC wave scattering with possible consequences for climate change mechanisms Reviewed

    B. T. Tsurutani, R. Hajra, T. Tanimori, A. Takada, R. Bhanu, A. J. Mannucci, G. S. Lakhina, J. U. Kozyra, K. Shiokawa, L. C. Lee, E. Echer, R. V. Reddy, W. D. Gonzalez

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 10 ) page: 10130 - 10156   2016.10

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    A new scenario is presented for the cause of magnetospheric relativistic electron decreases (REDs) and potential effects in the atmosphere and on climate. High-density solar wind heliospheric plasmasheet (HPS) events impinge onto the magnetosphere, compressing it along with remnant noon-sector outer-zone magnetospheric similar to 10-100 keV protons. The betatron accelerated protons generate coherent electromagnetic ion cyclotron (EMIC) waves through a temperature anisotropy (T-perpendicular to/T-|| &gt; 1) instability. The waves in turn interact with relativistic electrons and cause the rapid loss of these particles to a small region of the atmosphere. A peak total energy deposition of similar to 3 x 10(20) ergs is derived for the precipitating electrons. Maximum energy deposition and creation of electron-ion pairs at 30-50 km and at &gt; 30 km altitude are quantified. We focus the readers' attention on the relevance of this present work to two climate change mechanisms. Wilcox et al. (1973) noted a correlation between solar wind heliospheric current sheet (HCS) crossings and high atmospheric vorticity centers at 300 mb altitude. Tinsley et al. (1994) has constructed a global circuit model which depends on particle precipitation into the atmosphere. Other possible scenarios potentially affecting weather/climate change are also discussed.

    DOI: 10.1002/2016JA022499

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  125. Spectral characteristics of steady quiet-time EMIC waves observed at geosynchronous orbit Reviewed

    Kim Khan-Hyuk, Park Jong-Sun, Omura Yoshiharu, Shiokawa Kazuo, Lee Dong-Hun, Kim Gi-Jeong, Jin Ho, Lee Ensang, Kwon Hyuck-Jin

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 9 ) page: 8640-8660   2016.9

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    DOI: 10.1002/2016JA022957

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  126. Quasi-periodic rapid motion of pulsating auroras Reviewed

    Fukuda Yoko, Kataoka Ryuho, Miyoshi Yoshizumi, Katoh Yuto, Nishiyama Takanori, Shiokawa Kazuo, Ebihara Yusuke, Hampton Donald, Iwagami Naomoto

    POLAR SCIENCE   Vol. 10 ( 3 ) page: 183-191   2016.9

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    DOI: 10.1016/j.polar.2016.03.005

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  127. A proposal on the study of solar-terrestrial coupling processes with atmospheric radars and ground-based observation network Reviewed

    Tsuda Toshitaka, Yamamoto Mamoru, Hashiguchi Hiroyuki, Shiokawa Kazuo, Ogawa Yasunobu, Nozawa Satonori, Miyaoka Hiroshi, Yoshikawa Akimasa

    RADIO SCIENCE   Vol. 51 ( 9 ) page: 1587-1599   2016.9

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    DOI: 10.1002/2016RS006035

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  128. Direct observational evidence for the merging of equatorial plasma bubbles Reviewed

    V. L. Narayanan, S. Gurubaran, K. Shiokawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 8 ) page: 7923 - 7931   2016.8

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    In this work we present direct ground-based observational evidence for the merging of individual equatorial plasma bubbles (EPBs) obtained through the imaging of OI 630.0 nm airglow. Three potential mechanisms have been identified: (1) One of the EPBs tilts and reaches location of the adjacent growing EPB finally merging with it. (2) Some of the branches of an EPB arising from secondary instabilities reach out to adjacent EPB and merge with it. (3) The eastward zonal drift of the EPB on the eastern side slows down while the adjacent EPB on the western side drifts relatively faster and catches up. In one of the cases, a branch of an EPB was observed to get interchanged with another EPB as a result of merging and consequent pinching off from the parent EPB.

    DOI: 10.1002/2016JA022861

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  129. Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes Reviewed

    M. Ozaki, K. Shiokawa, Y. Miyoshi, R. Kataoka, S. Yagitani, T. Inoue, Y. Ebihara, C. -W Jun, R. Nomura, K. Sakaguchi, Y. Otsuka, M. Shoji, I. Schofield, M. Connors, V. K. Jordanova

    GEOPHYSICAL RESEARCH LETTERS   Vol. 43 ( 15 ) page: 7859 - 7866   2016.8

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    To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8s) images of proton-induced N-2(+) emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100s and an unpredicted fast modulation of a few tens of seconds. These results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.

    DOI: 10.1002/2016GL070008

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  130. Shrinking equatorial plasma bubbles Reviewed

    V. L. Narayanan, S. Gurubaran, K. Shiokawa, K. Emperumal

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 7 ) page: 6924 - 6935   2016.7

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    The formation of equatorial plasma bubbles (EPBs) associated with spread F irregularities are fairly common phenomenon in the postsunset equatorial ionosphere. These bubbles grow as a result of eastward polarization electric field resulting in upward ExB drift over the dip equator. As they grow they are also mapped to low latitudes along magnetic field lines. The EPBs are often observed as airglow depletions in the images of OI 630nm emission. On occasions the growth of the features over the dip equator is observed as poleward extensions of the depletions in all-sky images obtained from low latitudes. Herein, we present interesting observations of decrease in the latitudinal extent of the EPBs corresponding to a reduction in their apex altitudes over the dip equator. Such observations indicate that these bubbles not only grow but also shrink on occasions. These are the first observations of shrinking EPBs. The observations discussed in this work are based on all-sky airglow imaging observations of OI 630.0nm emission made from Panhala (11.1 degrees N dip latitude). In addition, ionosonde observations made from dip equatorial site Tirunelveli (1.1 degrees N dip latitude) are used to understand the phenomenon better. The analysis indicates that the speed of shrinking occurring in the topside is different from the bottomside vertical drifts. When the EPBs shrink, they might decay before sunrise hours.

    DOI: 10.1002/2016JA022633

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  131. ELF/VLF wave propagation at subauroral latitudes: Conjugate observation between the ground and Van Allen Probes A Reviewed

    Martinez-Calderon Claudia, Shiokawa Kazuo, Miyoshi Yoshizumi, Keika Kunihiro, Ozaki Mitsunori, Schofield Ian, Connors Martin, Kletzing Craig, Hanzelka Miroslav, Santolik Ondrej, Kurth William S.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 6 ) page: 5384-5393   2016.6

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    DOI: 10.1002/2015JA022264

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  132. Special issue "The 12th International Conference on Substorms"

    Shiokawa Kazuo, Fok Mei-Ching, Fujimoto Masaki

    EARTH PLANETS AND SPACE   Vol. 68   2016.5

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    DOI: 10.1186/s40623-016-0471-8

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  133. Possible generation mechanisms for Pc1 pearl structures in the ionosphere based on 6 years of ground observations in Canada, Russia, and Japan Reviewed

    Jun Chae-Woo, Shiokawa Kazuo, Connors Martin, Schofield Ian, Poddelsky Igor, Shevtsov Boris

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 5 ) page: 4409-4424   2016.5

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    DOI: 10.1002/2015JA022123

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  134. An evidence for prompt electric field disturbance driven by changes in the solar wind density under northward IMF B-z condition Reviewed

    Diptiranjan Rout, D. Chakrabarty, R. Sekar, G. D. Reeves, J. M. Ruohoniemi, Tarun K. Pant, B. Veenadhari, K. Shiokawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 5 ) page: 4800 - 4810   2016.5

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    Before the onset of a geomagnetic storm on 22 January 2012 (Ap = 24), an enhancement in solar wind number density from 10/cm(3) to 22/cm(3) during 0440-0510UT under northward interplanetary magnetic field (IMF B-z) condition is shown to have enhanced the high-latitude ionospheric convection and also caused variations in the geomagnetic field globally. Conspicuous changes in X are observed not only at longitudinally separated low-latitude stations over Indian (prenoon), South American (midnight), Japanese (afternoon), Pacific (afternoon) and African (morning) sectors but also at latitudinally separated stations located over high and middle latitudes. The latitudinal variation of the amplitude of the X during 0440-0510UT is shown to be consistent with the characteristics of prompt penetration electric field disturbances. Most importantly, the density pulse event caused enhancements in the equatorial electrojet strength and the peak height of the F layer (h(m)F(2)) over the Indian dip equatorial sector. Further, the concomitant enhancements in electrojet current and F layer movement over the dip equator observed during this space weather event suggest a common driver of prompt electric field disturbance at this time. Such simultaneous variations are found to be absent during magnetically quiet days. In absence of significant change in solar wind velocity and magnetospheric substorm activity, these observations point toward perceptible prompt electric field disturbance over the dip equator driven by the overcompression of the magnetosphere by solar wind density enhancement.

    DOI: 10.1002/2016JA022475

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  135. Lower thermospheric wind variations in auroral patches during the substorm recovery phase Reviewed

    Oyama Shin-ichiro, Shiokawa Kazuo, Miyoshi Yoshizumi, Hosokawa Keisuke, Watkins Brenton J., Kurihara Junichi, Tsuda Takuo T., Fallen Christopher T.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 4 ) page: 3564-3577   2016.4

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    DOI: 10.1002/2015JA022129

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  136. Coordinated observations of F region 3m field-aligned plasma irregularities associated with medium-scale traveling ionospheric disturbances Reviewed

    F. F. Lin, C. Y. Wang, C. L. Su, K. Shiokawa, S. Saito, Y. H. Chu

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 4 ) page: 3750 - 3766   2016.4

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    Three meter field-aligned irregularities (3m FAIs) associated with medium-scale traveling ionospheric disturbances (MSTIDs) that occurred on 5 February 2008 were observed by using the Chung-Li 52MHz coherent scatter radar. Interferometry measurements show that the plasma structures responsible for the 3m FAI echoes are in a clumpy shape with a horizontal dimension of about 10-78km in a height range of 220-300km. In order to investigate the dynamic behaviors of the plasma irregularities at different scales in the bottomside of F region, the VHF radar echo structures from the 3m FAIs combined with the 630 nm airglow images provided by the Yonaguni all-sky imager are compared and analyzed. The results show that the radar echoes were located at the west edge of the depletion zones of the 630 nm airglow image of the MSTIDs. The bulk echo structures of the 3m FAIs drifted eastward at a mean trace velocity of about 30m/s that is in general agreement with the zonal trace velocity of the MSTIDs shown in the 630nm airglow images. These results suggest that the observed F region 3m FAIs for the present case can be regarded as the targets that are frozen in the local region of theMSTIDs. In addition, the radar-observed 3mFAI echo intensity and spectral width bear high correlations to the percentage variations of the 630nm emission intensity. These results seem to suggest that through the nonlinear turbulence cascade process, theMSTID-associated 3mFAIs are very likely generated from the kilometer-scale plasma irregularities with large amplitude excited by the gradient drift instability.

    DOI: 10.1002/2016JA022511

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  137. Special issue "International CAWSES-II Symposium"

    Yamamoto Mamoru, Shiokawa Kazuo, Nakamura Takuji, Gopalswamy Nat

    EARTH PLANETS AND SPACE   Vol. 68   2016.2

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    DOI: 10.1186/s40623-016-0392-6

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  138. Altitude development of postmidnight F region field-aligned irregularities observed using Equatorial Atmosphere Radar in Indonesia Reviewed

    Tam Dao, Otsuka Yuichi, Shiokawa Kazuo, Ram S. Tulasi, Yamamoto Mamoru

    GEOPHYSICAL RESEARCH LETTERS   Vol. 43 ( 3 ) page: 1015-1022   2016.2

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    DOI: 10.1002/2015GL067432

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  139. EMIC waves observed at geosynchronous orbit under quiet geomagnetic conditions (Kp1) Reviewed

    J. -S. Park, K. -H. Kim, K. Shiokawa, D. -H. Lee, E. Lee, H. -J. Kwon, H. Jin, G. Jee

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 2 ) page: 1377 - 1390   2016.2

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    We statistically study the local time distribution of the helium band electromagnetic ion cyclotron (EMIC) waves observed at geosynchronous orbit when geomagnetic activity was low (Kp 1). In order to identify the geosynchronous EMIC waves, we use high time resolution magnetic field data acquired from GOES 10, 11, and 12 over a 2year period from 2007 and 2008 and examine the local time distribution of EMIC wave events. Unlike previous studies, which reported high EMIC wave occurrence in the postnoon sector with a peak around 1500-1600 magnetic local time (MLT) during magnetically disturbed times (i.e., storm and/or substorm), we observed that quiet time EMIC waves mostly occur in a region from morning (approximate to 0600MLT) to afternoon (approximate to 1600MLT) with a peak around 1100-1200MLT. To investigate whether the quiet time EMIC wave occurrence has a causal relationship with magnetospheric convection enhancement or solar wind dynamic pressure variations, we performed a superposed epoch analysis of solar wind parameters (solar wind speed, density, dynamic pressure, and interplanetary magnetic field B-z) and geomagnetic indices (AE and SYM-H). From the superposed epoch analysis we found that solar wind dynamic pressure variation is a more important parameter than AE and SYM-H for quiet time EMIC wave occurrence.

    DOI: 10.1002/2015JA021968

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  140. Longitudinal frequency variation of long-lasting EMIC Pc1-Pc2 waves localized in the inner magnetosphere Reviewed

    K. -H. Kim, K. Shiokawa, I. R. Mann, J. -S. Park, H. -J. Kwon, K. Hyun, H. Jin, M. Connors

    GEOPHYSICAL RESEARCH LETTERS   Vol. 43 ( 3 ) page: 1039 - 1046   2016.2

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    Long-lasting (&gt;20h) electromagnetic ion cyclotron (EMIC) Pc1-Pc2 waves were observed by the Athabasca (L =approximate to 4.6) induction magnetometer and Canadian Array for Realtime Investigations of Magnetic Activity (L =approximate to 4-6) fluxgate magnetometers on 5 April 2007. These waves showed a systematic frequency change with local time, the minimum frequency near dusk, and the maximum frequency near dawn. Assuming the plasmapause as a potential source region of the waves, we estimated the plasmapause location from localized proton enhancement (LPE) events observed at NOAA-Polar Orbiting Environmental Satellites and METOP-2 satellites. We found that the longitudinal frequency variation of EMIC waves has a clear correlation with the estimated plasmapause location and that the waves are in the frequency band between the equatorial helium and oxygen gyrofrequencies at the estimated plasmapause. With our analysis results we suggest that the LPE events are caused by wave-particle interaction with the helium band EMIC waves generated near the plasmapause.

    DOI: 10.1002/2015GL067536

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  141. Pulsating proton aurora caused by rising tone Pc1 waves Reviewed

    R. Nomura, K. Shiokawa, Y. Omura, Y. Ebihara, Y. Miyoshi, K. Sakaguchi, Y. Otsuka, M. Connors

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 2 ) page: 1608 - 1618   2016.2

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    We found rising tone emissions with a dispersion of approximate to 1Hz per several tens of seconds in the dynamic spectrum of a Pc1 geomagnetic pulsation (Pc1) observed on the ground. These Pc1 rising tones were successively observed over approximate to 30min from 0250UT on 14 October 2006 by an induction magnetometer at Athabasca, Canada (54.7 degrees N, 246.7 degrees E, magnetic latitude 61.7 degrees N). Simultaneously, a Time History of Events and Macroscale Interactions during Substorms panchromatic (THEMIS) all-sky camera detected pulsations of an isolated proton aurora with a period of several tens of seconds, approximate to 10% variations in intensity, and fine structures of 3 degrees in magnetic longitudes. The pulsations of the proton aurora close to the zenith of ATH have one-to-one correspondences with the Pc1 rising tones. This suggests that these rising tones scatter magnetospheric protons intermittently at the equatorial region. The radial motion of the magnetospheric source, of which the isolated proton aurora is a projection, can explain the central frequency increase of Pc1, but not the shorter period (tens of seconds) frequency increase of approximate to 1Hz in Pc1 rising tones. We suggest that EMIC-triggered emissions generate the frequency increase of Pc1 rising tones on the ground and that they also cause the Pc1 pearl structure, which has a similar characteristic time.

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  142. Duskside enhancement of equatorial zonal electric field response to convection electric fields during the St. Patrick's Day storm on 17 March 2015 Reviewed

    S. Tulasi Ram, T. Yokoyama, Y. Otsuka, K. Shiokawa, S. Sripathi, B. Veenadhari, R. Heelis, K. K. Ajith, V. S. Gowtam, S. Gurubaran, P. Supnithi, M. Le Huy

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 121 ( 1 ) page: 538 - 548   2016.1

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    The equatorial zonal electric field responses to prompt penetration of eastward convection electric fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F layer to &gt;550km and development of intense equatorial plasma bubbles (EPBs) were observed. These EPBs were found to extend up to 27.13 degrees N and 25.98 degrees S magnetic dip latitudes indicating their altitude development to similar to 1670km at apex. In contrast, at few degrees east in the premidnight sector (Thailand-Indonesian longitudes), no significant height rise and/or EPB activity has been observed. The eastward electric field perturbations due to PPEF are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo (IDD) fields, whereas they were mostly counter balanced by the IDD fields in the premidnight sector. In situ observations from SWARM-A and SWARM-C and Communication/Navigation Outage Forecasting System satellites detected a large plasma density depletion near Indian equatorial region due to large electrodynamic uplift of F layer to higher than satellite altitudes. Further, this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator. This study brings out the significantly enhanced equatorial zonal electric field in response to PPEF that is uniquely confined to dusk sector. The responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field B-z.

    DOI: 10.1002/2015JA021932

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  143. Isolated Proton Auroras and Pc1/EMIC Waves at Subauroral Latitudes Reviewed

    Sakaguchi Kaori, Shiokawa Kazuo, Miyoshi Yoshizumi, Connors Martin

    AURORAL DYNAMICS AND SPACE WEATHER   Vol. 215   page: 59 - 70   2016

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  144. Polar cap precursor of nightside auroral oval intensifications using polar cap arcs Reviewed

    Zou Ying, Nishimura Yukitoshi, Lyons Larry R., Donovan Eric F., Shiokawa Kazuo, Ruohoniemi J. Michael, McWilliams Kathryn A., Nishitani Nozomu

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 12 ) page: 10698-10711   2015.12

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    DOI: 10.1002/2015JA021816

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  145. Isolated Proton Auroras and Pc1/EMIC Waves at Subauroral Latitudes Reviewed

    Kaori Sakaguchi, Kazuo Shiokawa, Yoshizumi Miyoshi, Martin Connors

    Auroral Dynamics and Space Weather     page: 59 - 70   2015.11

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    Isolated proton aurora (IPA) in the subauroral ionosphere is created by energetic proton precipitation through wave-particle interactions with electromagnetic ion cyclotron (EMIC) waves in the conjugate inner magnetosphere. In this study, spatial distribution and occurrence probability of IPAs were statistically investigated as a proxy for regions of EMIC wave occurrence using ground-based imaging data during 2006-2012 at Athabasca, Canada. The 7-year average of the IPA occurrence probability over the total observation interval was estimated to be 0.83%, and a factor of 5 change was found between maximum and minimum years. Local time (between 16 and 06 MLT) distribution shows double peaks at premidnight and at dusk. The occurrence probability increases with Kp, and the MLT location tends to shift duskward. The statistical distribution of IPA size shows a clear peak at a spatial size of 10,000 km2, and latitudinal and longitudinal lengths have peaks at 56 and 340 km, respectively, at the ionospheric altitude. The equatorial projections of IPA source locations and two-dimensional (2D) structures are estimated by magnetic field tracing. These spatial structures are essential to quantitatively estimate the loss rate of energetic particles, contributing to space weather studies.

    DOI: 10.1002/9781118978719.ch5

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  146. A direct link between chorus emissions and pulsating aurora on timescales from milliseconds to minutes: A case study at subauroral latitudes Reviewed

    Ozaki Mitsunori, Yagitani Satoshi, Sawai Kaoru, Shiokawa Kazuo, Miyoshi Yoshizumi, Kataoka Ryuho, Ieda Akimasa, Ebihara Yusuke, Connors Martin, Schofield Ian, Katoh Yuto, Otsuka Yuichi, Sunagawa Naoki, Jordanova Vania K.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 11 ) page: 9617-9631   2015.11

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    DOI: 10.1002/2015JA021381

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  147. Coordinated airglow observations between IMAP/VISI and a ground-based all-sky imager on concentric gravity wave in the mesopause Reviewed

    S. Perwitasari, T. Sakanoi, A. Yamazaki, Y. Otsuka, Y. Hozumi, Y. Akiya, A. Saito, K. Shiokawa, S. Kawamura

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 11 ) page: 9706 - 9721   2015.11

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    We present a study of concentric gravity waves (CGWs) event from the coordinated observation between Ionosphere, Mesosphere, upper Atmosphere, and Plasmasphere mapping (IMAP)/Visible and near-Infrared Spectral Imager (VISI), all-sky camera at Rikubetsu, Multi-functional Transport Satellite (MTSAT), Tropical Rainfall Measuring Mission, and MF radar at Wakkanai combined with Modern-Era Retrospective Analysis for Research and Application data. IMAP/VISI is the first space-based imager that capable of imaging the airglow in the mesosphere and lower thermosphere region in the nadir-looking direction. Therefore, it has a unique ability to observe a great extend of CGWs propagation. Arc-like shaped, part of CGWs pattern was observed around themesopause (similar to 95 km) in the O-2 762 nm airglow emission obtained by IMAP/VISI at 1204 UT on 18 October 2012. Similar patterns were also observed by the all-sky imager at Rikubetsu (43.5 degrees N, 143.8 degrees E) in OI 557.7 nm and OH band airglow emissions from similar to 1100 to 1200 UT. Horizontal wavelengths of the observed small-scale gravity waves are similar to 50 km (OH band and OI 557.7nm) and similar to 67 km (O-2 762 nm). The source is suggested to be a deep convective activity over Honshu Island which likely was an enhanced convective activity related to a typhoon in the south of Japan. The data showed that the CGWs could propagate up to similar to 1400-1500km horizontally from the source to the mesopause but not farther away. Using atmospheric temperature profiles obtained by Thermospheric Ionosphere Mesosphere Energetics Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry, we conclude that this long-distance propagation of the waves could be caused by thermal duct in the middle atmosphere. The arc-like shaped instead of full circle pattern points out that the wind filtering effect is significant for the particular direction of wave propagation.

    DOI: 10.1002/2015JA021424

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  148. Spatiotemporally resolved electrodynamic properties of a Sun-aligned arc over Resolute Bay Reviewed

    G. W. Perry, H. Dahlgren, M. J. Nicolls, M. Zettergren, J. -P. St-Maurice, J. L. Semeter, T. Sundberg, K. Hosokawa, K. Shiokawa, S. Chen

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 11 ) page: 9977 - 9987   2015.11

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    Common volume measurements by the Resolute Bay Incoherent Scatter Radar-North (RISR-N) and Optical Mesosphere and Thermosphere Imagers (OMTI) have been used to clarify the electrodynamic structure of a Sun-aligned arc in the polar cap. The plasma parameters of the dusk-to-dawn drifting arc and surrounding ionosphere are extracted using the volumetric imaging capabilities of RISR-N. Multipoint line-of-sight RISR-N measurements of the plasma drift are inverted to construct a time sequence of the electric field and field-aligned current system of the arc. Evidence of dramatic electrodynamic and plasma structuring of the polar cap ionosphere due to the arc is described. One notable feature of the arc is a meridionally extended plasma density depletion on its leading edge, located partially within a downward field-aligned current region. The depletion is determined to be a by-product of enhanced chemical recombination operating on a time scale of 15 min. A similarly shaped electric field structure of over 100 mV/m and line-of-sight ion temperatures nearing 3000 K were collocated with the depletion.

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  149. Statistical study of ELF/VLF emissions at subauroral latitudes in Athabasca, Canada Reviewed

    Martinez-Calderon Claudia, Shiokawa Kazuo, Miyoshi Yoshizumi, Ozaki Mitsunori, Schofield Ian, Connors Martin

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 10 ) page: 8455-8469   2015.10

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    DOI: 10.1002/2015JA021347

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  150. On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations Reviewed

    T. Motoba, S. Ohtani, B. J. Anderson, H. Korth, D. Mitchell, L. J. Lanzerotti, K. Shiokawa, M. Connors, C. A. Kletzing, G. D. Reeves

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 10 ) page: 8707 - 8722   2015.10

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    Magnetotail processes and structures related to substorm growth phase/onset auroral arcs remain poorly understood mostly due to the lack of adequate observations. In this study we make a comparison between ground-based optical measurements of the premidnight growth phase/onset arcs at subauroral latitudes and magnetically conjugate measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) at 780km in altitude and by the Van Allen Probe B (RBSP-B) spacecraft crossing L values of 5.0-5.6 in the premidnight inner tail region. The conjugate observations offer a unique opportunity to examine the detailed features of the arc location relative to large-scale Birkeland currents and of the magnetospheric counterpart. Our main findings include (1) at the early stage of the growth phase the quiet auroral arc emerged 4.3 degrees equatorward of the boundary between the downward Region 2 (R2) and upward Region 1 (R1) currents; (2) shortly before the auroral breakup (poleward auroral expansion) the latitudinal separation between the arc and the R1/R2 demarcation narrowed to 1.0 degrees; (3) RBSP-B observed a magnetic field signature of a local upward field-aligned current (FAC) connecting the arc with the near-Earth tail when the spacecraft footprint was very close to the arc; and (4) the upward FAC signature was located on the tailward side of a local plasma pressure increase confined near L5.2-5.4. These findings strongly suggest that the premidnight arc is connected to highly localized pressure gradients embedded in the near-tail R2 source region via the local upward FAC.

    DOI: 10.1002/2015JA021676

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  151. Multi-instrument, high-resolution imaging of polar cap patch transportation Reviewed

    E. G. Thomas, K. Hosokawa, J. Sakai, J. B. H. Baker, J. M. Ruohoniemi, S. Taguchi, K. Shiokawa, Y. Otsuka, A. J. Coster, J. -P. St.-Maurice, K. A. McWilliams

    RADIO SCIENCE   Vol. 50 ( 9 ) page: 904 - 915   2015.9

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    Transionospheric radio signals in the high-latitude polar cap are susceptible to degradation when encountering sharp electron density gradients associated with discrete plasma structures, or patches. Multi-instrument measurements of polar cap patches are examined during a geomagnetic storm interval on 22 January 2012. For the first time, we monitor the transportation of patches with high spatial and temporal resolution across the polar cap for 1-2 h using a combination of GPS total electron content (TEC), all-sky airglow imagers (ASIs), and Super Dual Auroral Radar Network (SuperDARN) HF radar backscatter. Simultaneous measurements from these data sets allow for continuous tracking of patch location, horizontal extent, and velocity despite adverse observational conditions for the primary technique (e.g., sunlit regions in the ASI data). Spatial collocation between patch-like features in relatively coarse but global GPS TEC measurements and those mapped by high-resolution ASI data was very good, indicating that GPS TEC can be applied to track patches continuously as they are transported across the polar cap. In contrast to previous observations of cigar-shaped patches formed under weakly disturbed conditions, the relatively narrow dawn-dusk extent of patches in the present interval (500-800 km) suggests association with a longitudinally confined plasma source region, such as storm-enhanced density (SED) plume. SuperDARN observations show that the backscatter power enhancements corresponded to the optical patches, and for the first time we demonstrate that the motion of the optical patches was consistent with background plasma convection velocities.

    DOI: 10.1002/2015RS005672

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  152. Statistical study of auroral fragmentation into patches Reviewed

    Hashimoto Ayumi, Shiokawa Kazuo, Otsuka Yuichi, Oyama Shin-ichiro, Nozawa Satonori, Hori Tomoaki, Lester Mark, Johnsen Magnar Gullikstad

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 8 ) page: 6207-6217   2015.8

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    DOI: 10.1002/2015JA021000

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  153. Plasma bubble monitoring by TEC map and 630 nm airglow image Reviewed

    H. Takahashi, C. M. Wrasse, Y. Otsuka, A. Ivo, V. Gomes, I. Paulino, A. F. Medeiros, C. M. Denardini, N. Sant'Anna, K. Shiokawa

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 130   page: 151 - 158   2015.8

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

    Equatorial ionosphere plasma bubbles over the South American continent were successfully observed by mapping the total electron content (TECMAP) using data provided by ground-based GNSS receiver networks. The TECMAP could cover almost all of the continent within 4000 km distance in longitude and latitude, monitoring TEC variability continuously with a time resolution of 10 min. Simultaneous observations of OI 630 nm all-sky image at Cachoeira Paulista (22.7 degrees S, 45.0 degrees W) and Cariri (7.4 degrees S, 36.5 degrees W) were used to compare the bubble structures. The spatial resolution of the TECMAP varied from 50 km to 1000 km, depending on the density of the observation sites. On the other hand, optical imaging has a spatial resolution better than 15 km, depicting the fine structure of the bubbles but covering a limited area (similar to 1600 km diameter). TECMAP has an advantage in its spatial coverage and the continuous monitoring (day and night) form. The initial phase of plasma depletion in the post-sunset equatorial ionization anomaly (PS-EIA) trough region, followed by development of plasma bubbles in the crest region, could be monitored in a progressive way over the magnetic equator. In December 2013 to January 2014, periodically spaced bubble structures were frequently observed. The longitudinal spacing between the bubbles was around 600-800 km depending on the day. The periodic form of plasma bubbles may suggest a seeding process related to the solar terminator passage in the ionosphere. (C) 2015 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2015.06.003

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  154. Van Allen probes, NOAA, GOES, and ground observations of an intense EMIC wave event extending over 12 h in magnetic local time Reviewed

    M. J. Engebretson, J. L. Posch, J. R. Wygant, C. A. Kletzing, M. R. Lessard, C. -L. Huang, H. E. Spence, C. W. Smith, H. J. Singer, Y. Omura, R. B. Horne, G. D. Reeves, D. N. Baker, M. Gkioulidou, K. Oksavik, I. R. Mann, T. Raita, K. Shiokawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 7 ) page: 5465 - 5488   2015.7

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    Although most studies of the effects of electromagnetic ion cyclotron (EMIC) waves on Earth's outer radiation belt have focused on events in the afternoon sector in the outer plasmasphere or plume region, strong magnetospheric compressions provide an additional stimulus for EMIC wave generation across a large range of local times and L shells. We present here observations of the effects of a wave event on 23 February 2014 that extended over 8h in UT and over 12h in local time, stimulated by a gradual 4h rise and subsequent sharp increases in solar wind pressure. Large-amplitude linearly polarized hydrogen band EMIC waves (up to 25nT p-p) appeared for over 4h at both Van Allen Probes, from late morning through local noon, when these spacecraft were outside the plasmapause, with densities similar to 5-20cm(-3). Waves were also observed by ground-based induction magnetometers in Antarctica (near dawn), Finland (near local noon), Russia (in the afternoon), and in Canada (from dusk to midnight). Ten passes of NOAA-POES and METOP satellites near the northern foot point of the Van Allen Probes observed 30-80keV subauroral proton precipitation, often over extended L shell ranges; other passes identified a narrow L shell region of precipitation over Canada. Observations of relativistic electrons by the Van Allen Probes showed that the fluxes of more field-aligned and more energetic radiation belt electrons were reduced in response to both the emission over Canada and the more spatially extended emission associated with the compression, confirming the effectiveness of EMIC-induced loss processes for this event.

    DOI: 10.1002/2015JA021227

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  155. Resonance structure and mode transition of quarter-wave ULF pulsations around the dawn terminator Reviewed

    Obana Yuki, Waters Colin L., Sciffer Murray D., Menk Frederick W., Lysak Robert L., Shiokawa Kazuo, Hurst Anthony W., Petersen Tanja

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 6 ) page: 4194-4212   2015.6

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    DOI: 10.1002/2015JA021096

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  156. Three different types of electric field disturbances affecting equatorial ionosphere during a long-duration prompt penetration event Reviewed

    D. Chakrabarty, Diptiranjan Rout, R. Sekar, R. Narayanan, G. D. Reeves, Tarun K. Pant, B. Veenadhari, K. Shiokawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 6 ) page: 4993 - 5008   2015.6

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    Coordinated digisonde and OI 630.0nm airglow observations from Thumba (TVM), an Indian dip equatorial station, in conjunction with magnetic and geosynchronous particle flux measurements, reveal three different types of electric field disturbances in the equatorial ionosphere-thermosphere system (ITS) occurring in succession over a period of 6h on a single night (22-23 January,2012; A(p) = 24). These include (1) westward electric field perturbations owing to a pseudo-breakup and a substorm event, each lasting for about 30min; (2) eastward electric field perturbations continuing for about an hour, owing to the southward excursion of Z component of interplanetary magnetic field (B-z); and (3) DP2-type fluctuating (period approximate to 40min) electric field perturbation sustaining for about 4h. The pseudo-breakup and the fully grown substorm events are found to be longitudinally localized and different in terms of response in the westward auroral electrojet index (AL) as well as geosynchronous electron/proton injections. The polarity of the prompt penetration of interplanetary electric field that affects the equatorial ionosphere is observed to be eastward during 2100-2200 IST (Indian Standard Time) which is observationally sparse but consistent with modeling studies. Interestingly, on the same night, DP2-type electric field fluctuations with approximate to 40min periodicity and occasional eastward polarity (akin to daytime) are also found to affect the equatorial ITS for about 4h (2200-0200 IST). The case study, thus, brings out different processes that constitute a long duration prompt penetration event which, otherwise, would have been categorized as a single event.

    DOI: 10.1002/2014JA020759

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  157. Localized polar cap flow enhancement tracing using airglow patches: Statistical properties, IMF dependence, and contribution to polar cap convection Reviewed

    Zou Ying, Nishimura Yukitoshi, Lyons Larry R., Shiokawa Kazuo, Donovan Eric F., Ruohoniemi J. Michael, McWilliams Kathryn A., Nishitani Nozomu

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 5 ) page: 4064-4078   2015.5

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    DOI: 10.1002/2014JA020946

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  158. Airglow-imaging observation of plasma bubble disappearance at geomagnetically conjugate points Reviewed

    Shiokawa Kazuo, Otsuka Yuichi, Lynn Kenneth J. W., Wilkinson Philip, Tsugawa Takuya

    EARTH PLANETS AND SPACE   Vol. 67   page: 1-12   2015.3

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    DOI: 10.1186/s40623-015-0202-6

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  159. Geomagnetically conjugate observation of plasma bubbles and thermospheric neutral winds at low latitudes Reviewed

    D. Fukushima, K. Shiokawa, Y. Otsuka, M. Nishioka, M. Kubota, T. Tsugawa, T. Nagatsuma, S. Komonjinda, C. Y. Yatini

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 3 ) page: 2222 - 2231   2015.3

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    This is the first paper that reports simultaneous observations of zonal drift of plasma bubbles and the thermospheric neutral winds at geomagnetically conjugate points in both hemispheres. The plasma bubbles were observed in the 630nm nighttime airglow images taken by using highly sensitive all-sky airglow imagers at Kototabang, Indonesia (geomagnetic latitude (MLAT): 10.0 degrees S), and Chiang Mai, Thailand (MLAT: 8.9 degrees N), which are nearly geomagnetically conjugate stations, for 7h from 13 to 20UT (from 20 to 03LT) on 5 April 2011. The bubbles continuously propagated eastward with velocities of 100-125m/s. The 630nm images at Chiang Mai and those mapped to the conjugate point of Kototabang fit very well, which indicates that the observed plasma bubbles were geomagnetically connected. The eastward thermospheric neutral winds measured by two Fabry-Perot interferometers were 70-130m/s at Kototabang and 50-90m/s at Chiang Mai. We compared the observed plasma bubble drift velocity with the velocity calculated from the observed neutral winds and the model conductivity, to investigate the F region dynamo contribution to the bubble drift velocity. The estimated drift velocities were 60-90% of the observed velocities of the plasma bubbles, suggesting that most of the plasma bubble velocity can be explained by the F region dynamo effect.

    DOI: 10.1002/2014JA020398

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  160. CDF data archive and integrated data analysis platform for ERG-related ground data developed by ERG Science Center (ERG-SC) Reviewed

    Hori, T, Y. Miyashita, Y. Miyoshi, K. Seki, T. Segawa, Y.-M. Tanaka, K. Keika, M. Shoji, I. Shinohara, K. Shiokawa, Y. Otsuka, S. Abe, A. Yoshikawa, K. Yumoto, Y. Obana, N. Nishitani, A. S. Yukimatu, T. Nagatsuma, M. Kunitake, K. Hosokawa, Y. Ogawa, K. T. Murata, M. Nose, H. Kawano, T. Sakanoi

    J. Sp. Sci. Info. Jpn.   Vol. 4 (JAXA-RR-14-009)   page: 75 - 89   2015.3

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    The Exploration of energization and Radiation in Geospace project Science Center (ERG-SC) has developed the science data file archive and integrated data analysis tool for the ground network observation data of the ERG project. We have organized data design consortiums to develop and elaborate the standard metadata and data variable sets for each type of the ERG-related ground data being archived as Common Data Format (CDF) files. The integrated data analysis software for the project has also been developed on the basis of the Space Physics Environment Data Analysis Software (SPEDAS) which works in concert with the CDF data file repository. The software tools, which are provided as plug-in libraries for SPEDAS, are made available to the international science community so that scientists and students are ready to proceed to integrated studies combining the ground data with other satellite and simulation data seamlessly. The integrated data analysis software can make scientific activities more productive and help the ERG project achieve the scientific goals.

  161. Polarization analysis of VLF/ELF waves observed at subauroral latitudes during the VLF-CHAIN campaign Reviewed

    Martinez-Calderon Claudia, Shiokawa Kazuo, Miyoshi Yoshizumi, Ozaki Mitsunori, Schofield Ian, Connors Martin

    EARTH PLANETS AND SPACE   Vol. 67   2015.2

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    DOI: 10.1186/s40623-014-0178-7

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  162. The geospace response to variable inputs from the lower atmosphere: a review of the progress made by Task Group 4 of CAWSES-II Reviewed

    Oberheide Jens, Shiokawa Kazuo, Gurubaran Subramanian, Ward William E., Fujiwara Hitoshi, Kosch Michael J., Makela Jonathan J., Takahashi Hisao

    PROGRESS IN EARTH AND PLANETARY SCIENCE   Vol. 2   2015.2

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    DOI: 10.1186/s40645-014-0031-4

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  163. Daytime tweek atmospherics Reviewed

    Ohya Hiroyo, Shiokawa Kazuo, Miyoshi Yoshizumi

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 120 ( 1 ) page: 654-665   2015.1

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    DOI: 10.1002/2014JA020375

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  164. Airglow-imaging observation of plasma bubble disappearance at geomagnetically conjugate points Reviewed

    Shiokawa, K., Y. Otsuka, K. J. Lynn, P. Wilkinson, and T. Tsugawa

    Earth Planets and Space   Vol. 67 ( 43 )   2015

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    DOI: 10.1186/s40623-015-0202-6

  165. A statistical study of satellite traces and evolution of equatorial spread F Reviewed

    Narayanan Viswanathan Lakshmi, Sau Sukanta, Gurubaran Subramanian, Shiokawa Kazuo, Balan Nanan, Emperumal Kaliappan, Sripathi Samireddipalle

    EARTH PLANETS AND SPACE   Vol. 66   2014.12

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    DOI: 10.1186/s40623-014-0160-4

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  166. CME front and severe space weather Reviewed

    N. Balan, R. Skoug, S. Tulasi Ram, P. K. Rajesh, K. Shiokawa, Y. Otsuka, I. S. Batista, Y. Ebihara, T. Nakamura

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 12 ) page: 10,041 - 10,058   2014.12

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    Thanks to the work of a number of scientists who made it known that severe space weather can cause extensive social and economic disruptions in the modern high-technology society. It is therefore important to understand what determines the severity of space weather and whether it can be predicted. We present results obtained from the analysis of coronal mass ejections (CMEs), solar energetic particle (SEP) events, interplanetary magnetic field (IMF), CME-magnetosphere coupling, and geomagnetic storms associated with the major space weather events since 1998 by combining data from the ACE and GOES satellites with geomagnetic parameters and the Carrington event of 1859, the Quebec event of 1989, and an event in 1958. The results seem to indicate that (1) it is the impulsive energy mainly due to the impulsive velocity and orientation of IMF B-z at the leading edge of the CMEs (or CME front) that determine the severity of space weather. (2) CMEs having high impulsive velocity (sudden nonfluctuating increase by over 275 km s(-1) over the background) caused severe space weather (SvSW) in the heliosphere (failure of the solar wind ion mode of Solar Wind Electron Proton Alpha Monitor in ACE) probably by suddenly accelerating the high-energy particles in the SEPs ahead directly or through the shocks. (3) The impact of such CMEs which also show the IMF B-z southward from the leading edge caused SvSW at the Earth including extreme geomagnetic storms of mean Dst(MP) &lt; -250 nT during main phases, and the known electric power outages happened during some of these SvSW events. (4) The higher the impulsive velocity, the more severe the space weather, like faster weather fronts and tsunami fronts causing more severe damage through impulsive action. (5) The CMEs having IMF B-z northward at the leading edge do not seem to cause SvSW on Earth, although, later when the IMF B-z turns southward, they can lead to super geomagnetic storms of intensity (Dst(min)) less than even -400 nT.

    DOI: 10.1002/2014JA020151

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  167. Airglow observations of nighttime medium-scale traveling ionospheric disturbances from Yonaguni: Statistical characteristics and low-latitude limit Reviewed

    V. Lakshmi Narayanan, K. Shiokawa, Y. Otsuka, S. Saito

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 11 ) page: 9268 - 9282   2014.11

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    The characteristics of nighttime medium-scale traveling ionospheric disturbance (MSTID) features observed over Yonaguni (24.5 degrees N, 123.0 degrees E; 19.3 degrees N dip latitude), Japan are studied using all-sky imaging of OI 630.0nm airglow emission. The uniqueness of these observations is that the area observed by the imager covers the transition region between low to middle latitudes in the ionosphere. Typical low-latitude limit of midlatitude-type nighttime MSTIDs possessing phase front alignments along the northwest to the southeast occurs in this region. These MSTID features are rarely sighted at dip latitudes below 15 degrees. We selected 2 year period for analysis in which 1 year corresponded to the solar minimum conditions and another year to the solar maximum conditions. The MSTIDs were observed to extend to farther lower latitudes during the solar minimum conditions than during the solar maximum periods. Their observed range of wavelengths, phase velocities, phase front alignment, and propagation directions are similar to those observed at typical midlatitude sites. However, on many occasions the phase fronts of the observed MSTIDs did not extend over the whole field of view of the imager indicating that some process inhibits their extension to further lower latitudes. Detailed investigation suggests that the poleward propagating enhancement of airglow intensity, probably associated with the midnight pressure bulge, causes the MSTID features to disappear when they reach lower latitudes later in the night. When the MSTIDs reach lower latitudes well before midnight, they are found to be inhibited by the equatorial ionization anomaly crest region.

    DOI: 10.1002/2014JA020368

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  168. Traveling planetary wave activity from mesopause region airglow temperatures determined by the Network for the Detection of Mesospheric Change (NDMC) Reviewed

    E. R. Reisin, J. Scheer, M. E. Dyrland, F. Sigernes, C. S. Deehr, C. Schmidt, K. Hoeppner, M. Bittner, P. P. Ammosov, G. A. Gavrilyeva, J. Stegman, V. I. Perminov, A. I. Semenov, P. Knieling, R. Koppmann, K. Shiokawa, R. P. Lowe, M. J. Lopez-Gonzalez, E. Rodriguez, Y. Zhao, M. J. Taylor, R. A. Buriti, P. J. Espy, W. J. R. French, K. -U. Eichmann, J. P. Burrows, C. von Savigny

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 119   page: 71 - 82   2014.11

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    The global distribution of traveling planetary wave (PW) activity in the mesopause region is estimated for the first time from ground-based airglow measurements. Monthly and total mean climatologies of PW power are determined from rotational temperatures measured at 19 sites from 78 degrees N to 76 degrees S which contribute to the Network for the Detection of Mesospheric Change (NDMC). Wave power is expressed as the standard deviation of nocturnal mean temperature around the seasonal temperature variation. The results from 20 degrees N confirm the SABER traveling PW proxy by Offermann et al. (2009, J. Geophys. Res. 114, D06110) at two altitudes. Most sites between 69 degrees S and 69 degrees N show total mean traveling PW activity of about 6 K, and only some high latitude sites have considerably higher activity levels. At the two tropical sites, there is practically no seasonal variation of PW activity. At 70% of the midlatitude sites, the seasonal variation is moderate for most of the year, but it is quite appreciable at all high latitude sites. Results about traveling PW activity at 87 km and 95 km available from several sites signal similar behavior at both altitudes. The total mean climatological results here obtained have further been used to separate the traveling PW contribution from the superposition of wave types contained in OH rotational temperature fluctuations measured by the SCIAMACHY instrument on Envisat. A narrow equatorial wave activity maximum is probably caused by gravity waves, while a tendency towards greater activity at higher northern latitudes may be due to stationary planetary waves. (C) 2014 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2014.07.002

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  169. Auroral Physics in the Earth's Magnetosphere Reviewed

    SHIOKAWA Kazuo

      Vol. 90 ( 11 ) page: 708-712   2014.11

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  170. Study of Pc1 pearl structures observed at multi-point ground stations in Russia, Japan, and Canada Reviewed

    Jun Chae-Woo, Shiokawa Kazuo, Connors Martin, Schofield Ian, Poddelsky Igor, Shevtsov Boris

    EARTH PLANETS AND SPACE   Vol. 66   2014.10

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    DOI: 10.1186/s40623-014-0140-8

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  171. Auroral fragmentation into patches Reviewed

    Shiokawa, K., A. Hashimoto, T. Hori, K. Sakaguchi, Y. Ogawa, E. Donovan, E. Spanswick, M. Connors, Y. Otsuka, S.-I. Oyama, S. Nozawa, K. McWilliams

    Journal of Geophysical Research   Vol. 119   2014.10

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    DOI: doi:10.1029/2014JA020050

  172. Auroral fragmentation into patches Reviewed

    Shiokawa Kazuo, Hashimoto Ayumi, Hori Tomoaki, Sakaguchi Kaori, Ogawa Yasunobu, Donovan Eric, Spanswick Emma, Connors Martin, Otsuka Yuichi, Oyama Shin-Ichiro, Nozawa Satonori, McWilliams Kathryn

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 10 ) page: 8249-8261   2014.10

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    DOI: 10.1002/2014JA020050

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  173. 3D imaging reveals electrodynamics of polar cap aurora Reviewed

    Dahlgren Hanna, Perry Gareth, St Maurice Jean-Pierre, Sundberg Torbjorn, Hosokawa Keisuke, Semeter Joshua L., Nicolls Michael J., Shiokawa Kazuo

    ASTRONOMY & GEOPHYSICS   Vol. 55 ( 5 ) page: .   2014.10

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  174. 3D imaging reveals electrodynamics of polar cap aurora Reviewed

    Hanna Dahlgren, Gareth Perry, Jean-Pierre St Maurice, Torbjorn Sundberg, Keisuke Hosokawa, Joshua L. Semeter, Michael J. Nicolls, Kazuo Shiokawa

    ASTRONOMY & GEOPHYSICS   Vol. 55 ( 5 ) page: 5.26 - 5.28   2014.10

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    DOI: 10.1093/astrogeo/atu215

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  175. Ground-based ELF/VLF chorus observations at subauroral latitudes-VLF-CHAIN Campaign Reviewed

    Shiokawa Kazuo, Yokoyama Yu, Ieda Akimasa, Miyoshi Yoshizumi, Nomura Reiko, Lee Sungeun, Sunagawa Naoki, Miyashita Yukinaga, Ozaki Mitsunori, Ishizaka Kazumasa, Yagitani Satoshi, Kataoka Ryuho, Tsuchiya Fuminori, Schofield Ian, Connors Martin

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 9 )   2014.9

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    DOI: 10.1002/2014JA020161

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  176. Ground-based ELF/VLF chorus observations at subauroral latitudes - VLF-CHAIN Campaign Reviewed

    Shiokawa, K., Y. Yokoyama, A. Ieda, Y. Miyoshi, R. Nomura, S. Lee, N. Sunagawa, Y. Miyashita, M. Ozaki, K. Ishizaka, S. Yagitani, R. Kataoka, F. Tsuchiya, I. Schofield, and M. Connors

    Journal of Geophysical Research   Vol. 119   2014.8

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    DOI: 10.1029/2014JA020161

  177. New statistical analysis of the horizontal phase velocity distribution of gravity waves observed by airglow imaging Reviewed

    Takashi S. Matsuda, Takuji Nakamura, Mitsumu K. Ejiri, Masaki Tsutsumi, Kazuo Shiokawa

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES   Vol. 119 ( 16 ) page: 9707 - 9718   2014.8

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    We have developed a new analysis method for obtaining the power spectrum in the horizontal phase velocity domain from airglow intensity image data to study atmospheric gravity waves. This method can deal with extensive amounts of imaging data obtained on different years and at various observation sites without bias caused by different event extraction criteria for the person processing the data. The new method was applied to sodium airglow data obtained in 2011 at Syowa Station (69 degrees S, 40 degrees E), Antarctica. The results were compared with those obtained from a conventional event analysis in which the phase fronts were traced manually in order to estimate horizontal characteristics, such as wavelengths, phase velocities, and wave periods. The horizontal phase velocity of each wave event in the airglow images corresponded closely to a peak in the spectrum. The statistical results of spectral analysis showed an eastward offset of the horizontal phase velocity distribution. This could be interpreted as the existence of wave sources around the stratospheric eastward jet. Similar zonal anisotropy was also seen in the horizontal phase velocity distribution of the gravity waves by the event analysis. Both methods produce similar statistical results about directionality of atmospheric gravity waves. Galactic contamination of the spectrum was examined by calculating the apparent velocity of the stars and found to be limited for phase speeds lower than 30m/s. In conclusion, our new method is suitable for deriving the horizontal phase velocity characteristics of atmospheric gravity waves from an extensive amount of imaging data.

    DOI: 10.1002/2014JD021543

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  178. Diagnostics of equatorial and low latitude ionosphere by TEC mapping over Brazil Reviewed

    H. Takahashi, S. Costa, Y. Otsuka, K. Shiokawa, J. F. G. Monico, E. Paula, P. Nogueira, C. M. Denardini, F. Becker-Guedes, C. M. Wrasse, A. S. Ivo, V. C. F. Gomes, W. Gargarela, N. Sant'Anna, R. Gatto

    ADVANCES IN SPACE RESEARCH   Vol. 54 ( 3 ) page: 385 - 394   2014.8

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    The total electron content (TEC) in the equatorial and low-latitude ionosphere over Brazil was monitored in two dimensions by using 2011 data from the ground-based global navigation satellite system (GNSS) receiver network operated by the Brazilian Institute for Geography and Statistics. It was possible to monitor the spatial and temporal variations in TEC over Brazil continuously during both day and night with a temporal interval of 10 mm and a spatial resolution of about 400 km. The daytime equatorial ionization anomaly (ETA) and post-sunset plasma enhancement (PS-ETA) were monitored over an area corresponding to a longitudinal extension of 4000 km in South America. Considerable day-to-day variation was observed in ETA and PS-ETA. A large latitudinal and longitudinal gradient of TEC indicated a significant ionospheric range error in application of the GNSS positioning system. Large-scale plasma bubbles after sunset were also mapped over a wide range. Depletions with longitudinally separated by more than 800 km were observed. They were extended by more than 2000 km along the magnetic field lines and drifted eastward. It is expected that 2-dimensional TEC mapping can serve as a useful tool for diagnosing ionospheric weather, such as temporal and spatial variation in the equatorial plasma trough and crest, and particularly for monitoring the dynamics of plasma bubbles. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.asr.2014.01.032

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  179. Day-night coupling by a localized flow channel visualized by polar cap patch propagation Reviewed

    Y. Nishimura, L. R. Lyons, Y. Zou, K. Oksavik, J. I. Moen, L. B. Clausen, E. F. Donovan, V. Angelopoulos, K. Shiokawa, J. M. Ruohoniemi, N. Nishitani, K. A. McWilliams, M. Lester

    GEOPHYSICAL RESEARCH LETTERS   Vol. 41 ( 11 ) page: 3701 - 3709   2014.6

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    We present unique coordinated observations of the dayside auroral oval, polar cap, and nightside auroral oval by three all-sky imagers, two Super Dual Auroral Radar Network (SuperDARN) radars, and Defense Meteorological Satellite Program (DMSP)-17. This data set revealed that a dayside poleward moving auroral form (PMAF) evolved into a polar cap airglow patch that propagated across the polar cap and then nightside poleward boundary intensifications (PBIs). SuperDARN observations detected fast antisunward flows associated with the PMAF, and the DMSP satellite, whose conjunction occurred within a few minutes after the PMAF initiation, measured enhanced low-latitude boundary layer precipitation and enhanced plasma density with a strong antisunward flow burst. The polar cap patch was spatially and temporally coincident with a localized antisunward flow channel. The propagation across the polar cap and the subsequent PBIs suggests that the flow channel originated from dayside reconnection and then reached the nightside open-closed boundary, triggering localized nightside reconnection and flow bursts within the plasma sheet.

    DOI: 10.1002/2014GL060301

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  180. Deducing Locations and Charge Moment Changes of Lightning Discharges by ELF Network Observations in Japan Reviewed

    Y. Hobara, T. Inoue, M. Hayakawa, K. Shiokawa

    ICAE2014   Vol. ** ( ** ) page: ** - **   2014.6

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  181. Height-dependent ionospheric variations in the vicinity of nightside poleward expanding aurora after substorm onset Reviewed

    S. Oyama, Y. Miyoshi, K. Shiokawa, J. Kurihara, T. T. Tsuda, B. J. Watkins

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 5 ) page: 4146 - 4156   2014.5

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    High-latitude ionospheric variations at times near auroral substorms exhibit large temporal variations in both vertical and horizontal extents. Statistical analysis was made of data from the European Incoherent Scatter UHF radar at TromsO, Norway, and International Monitor for Auroral Geomagnetic Effects magnetometer for finding common features in electron density, ion and electron temperatures and relating these to currents and associated heating. This paper particularly focused on the height dependencies. Results show clear evidences of large electric field with corresponding frictional heating and Pedersen currents located just outside the front of the poleward expanding aurora, which typically appeared at the eastside of westward traveling surge. At the beginning of the substorm recovery phase, the ionospheric density had a large peak in the E region and a smaller peak in the F region. This structure was named as C form in this paper based on its shape in the altitude-time plot. The lower altitude density maximum is associated with hard auroral electron precipitation probably during pulsating aurora. We attribute the upper F region density maximum to local ionization by lower energy particle precipitation and/or long-lived plasma that is convected horizontally into the overhead measurement volume from the dayside hemisphere.

    DOI: 10.1002/2013JA019704

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  182. Pi2 pulsation simultaneously observed in the E and F region ionosphere with the SuperDARN Hokkaido radar Reviewed

    M. Teramoto, N. Nishitani, V. Pilipenko, T. Ogawa, K. Shiokawa, T. Nagatsuma, A. Yoshikawa, D. Baishev, K. T. Murata

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 119 ( 5 ) page: 3444 - 3462   2014.5

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    We investigated Pi2 pulsations in the nightside ionosphere that began at 14:15 UT (2315 LT) on 11 July 2010, and they were observed with high-temporal (8s) resolution by beam 4 of the Super Dual Auroral Radar Network (SuperDARN) Hokkaido radar. These pulsations were simultaneously observed in both the ground/sea scatter echoes reflected from the F region height and in ionospheric echoes from field-aligned irregularities in the sporadic Es region. They had the same period of 110s and approximately no phase lag. From the radar observations and the International Geomagnetic Reference Field model, the amplitude of the eastward (EEW) component of the electric field of the Pi2 pulsations in the ionosphere was estimated similar to 8.0mV/m in the F region and similar to 2.0mV/m in the E region. Corresponding Pi2 pulsations appeared dominantly in the horizontal northward magnetic field component (H) at nearby ground stations, Moshiri (MSR), St. Paratunka (PTK), and Stecolny (STC), with amplitudes ranging from 6 nT (MSR) to 10 nT (STC). At the dominant frequency of 8.8 mHz, the coherences between H and EEW were high (&gt;0.9), the cross phases of EEW relative to H were -56 degrees and -45 degrees, and the amplitude ratios were 2.7x105m/s and 8.4x105m/s, in the E and F regions, respectively. Based on a comparison of these results with theoretical predictions, we suggest that the concept of a pure cavity mode is not sufficient to explain the combined observations for midlatitude Pi2 waves and that the contribution of an Alfven waves must be taken in account.

    DOI: 10.1002/2012JA018585

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  183. Global imaging of polar cap patches with dual airglow imagers Reviewed

    K. Hosokawa, S. Taguchi, K. Shiokawa, Y. Otsuka, Y. Ogawa, M. Nicolls

    GEOPHYSICAL RESEARCH LETTERS   Vol. 41 ( 1 ) page: 1 - 6   2014.1

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    During a 2 h interval from 2240 to 2440 UT on 12 November 2012, regions of increased 630.0 nm airglow emissions were simultaneously detected by dual all-sky imagers in the polar cap, one at Longyearbyen, Norway (78.1 degrees N, 15.5 degrees E) and the other at Resolute Bay, Canada (74.7 degrees N, 265.1 degrees E). The Resolute Bay incoherent scatter radar observed clear enhancements of the F region electron density up to 10(12) m(-3) within these airglow structures which indicates that these are optical manifestations of polar cap patches propagating across the polar cap. During this interval of simultaneous airglow imaging, the nightside/dawnside (dayside/duskside) half of the patches was captured by the imager at Longyearbyen (Resolute Bay). This unique situation enabled us to estimate the dawn-dusk extent of the patches to be around 1500 km, which was at least 60-70% of the width of the antisunward plasma stream seen in the Super Dual Auroral Radar Network convection maps. In contrast to the large extent in the dawn-dusk direction, the noon-midnight thickness of each patch was less than 500 km. These observations demonstrate that there exists a class of patches showing cigar-shaped structures. Such patches could be produced in a wide range of local time on the dayside nearly simultaneously and spread across many hours of local time soon after their generation.

    DOI: 10.1002/2013GL058748

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  184. Deducing Locations and Electrical properties of Lightning Discharges by ELF Network Observations in Japan Reviewed

    Hobara Yasuhide, Hayaka Masashi, Shiokawa Kazuo

    2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS)     page: .   2014

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  185. Latitudinal variation of stochastic properties of the geomagnetic field Reviewed

    Wanliss J. A., Shiokawa K., Yumoto K.

    NONLINEAR PROCESSES IN GEOPHYSICS   Vol. 21 ( 2 ) page: 347-356   2014

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    DOI: 10.5194/npg-21-347-2014

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  186. P130 広域多地点大気光観測による中間圏大気重力波(ポスター・セッション) Reviewed

    鈴木 臣, 塩川 和夫, 大塚 雄一, 川村 誠治, 村山 泰啓

    大会講演予講集   Vol. 106   page: .   2014

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  187. Deducing locations and charge moment changes of lightning discharges by ELF network observations in Japan Reviewed

    Hobara Y., Inoue T., Hayakawa M., Shiokawa K.

    International Conference on Atmospheric Electricity, ICAE 2014     2014

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    Recent observations of electromagnetic radiations from lightning in the ELF frequency range so-called ELF transients are recognized as a powerful tool not only to deduce the global lightning distribution but also to obtain one of the most important properties of lightning discharges such as charge moment changes (CMCs). In this paper we demonstrate the spatio-temporal distributions of lightning discharges together with CMCs around Japan by using our newly developed domestic ELF observation network. This is the first time to obtain such type of distribution by using only ELF observations in the spatial scale of Japan (a few thousands km). We found that the obtained lightning source distributions both over the Pacific Ocean and the Sea of Japan are originated from the thunderstorm active regions confirmed by other measurements such as WWLLN. Statistical properties of the charge moment changes indicate that both number and CMC of positive CGs are superior to those of negative CGs. Moreover, considerably large CMC with both polarities are identified for the CGs over the Pacific Ocean as well as those with positive polarity over the Sea of Japan. Furthermore, we are going to present updated our lightning measurement network in Japan.

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  188. Deducing Locations and Electrical properties of Lightning Discharges by ELF Network Observations in Japan Reviewed

    Yasuhide Hobara, Masashi Hayaka, Kazuo Shiokawa

    2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS)     2014

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  189. Ground-Based Observations of Hiss-Like Emissions Changed from Chorus Emissions and Related Pulsating Aurora Reviewed

    Ozaki M., Sawai K., Yagitani S., Shiokawa K., Miyoshi Y., Kataoka R., Ieda A., Ebihara Y., Katoh Y.

    2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS)     2014

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  190. Ground-Based Observations of Hiss-Like Emissions Changed from Chorus Emissions and Related Pulsating Aurora Reviewed

    M. Ozaki, K. Sawai, S. Yagitani, K. Shiokawa, Y. Miyoshi, R. Kataoka, A. Ieda, Y. Ebihara, Y. Katoh

    2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS)     2014

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  191. Deducing locations and charge moment changes of lightning discharges by ELF network observations in Japan Reviewed

    Hobara Y.

    IEEJ Transactions on Power and Energy   Vol. 133 ( 12 ) page: 994 - 1000   2013.12

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    DOI: 10.1541/ieejpes.133.994

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    CiNii Article

  192. イオノゾンデおよびファブリ・ペロー干渉計によって観測された子午面熱圏風の比較 Reviewed

    西岡 未知, 丸山 隆, 大塚 雄一, 津川 卓也, 石橋 弘光, 塩川 和夫, 石井 守

    南極資料   Vol. 57 ( 3 ) page: 357-368   2013.11

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    電離圏ダイナミクスに大きく寄与する熱圏風についての理解を深めるため,イオノゾンデの磁気共役点観測により推定された南北方向の熱圏風(推定熱圏風)と,ファブリ・ペロー干渉計(FPI)観測により直接測定された南北方向の熱圏風との相関を調べた.推定熱圏風は,磁気共役点における熱圏風は等しい(赤道横断風モードが卓越する)という仮定のもとで導出される.2 つの手法で観測された夜間の熱圏風を比較するのは本研究が初めてである.2010 年のチェンマイ(タイ)とコトタバン(インドネシア)のイオノゾンデとFPI データを比較した結果,両者はおおむね良い相関を示したが,相関が悪い日もあった.相関が悪い事例は,赤道から収束・発散する成分を無視できず,赤道横断風モードが卓越するという仮定が成立しないと解釈されるものである.また,2 つの手法で求めた熱圏風の相関を季節別に調べると,2-4 月に両者の相関が高い一方,5-7 月に両者の相関が低いことがわかった.

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  193. Typhoon-induced concentric airglow structures in the mesopause region Reviewed

    S. Suzuki, S. L. Vadas, K. Shiokawa, Y. Otsuka, S. Kawamura, Y. Murayama

    GEOPHYSICAL RESEARCH LETTERS   Vol. 40 ( 22 ) page: 5983 - 5987   2013.11

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    We present the first reported gravity wave patterns in the mesopause region caused by a typhoon in the troposphere. On 10 December 2002, concentric rings of gravity waves in OH airglow were observed simultaneously by all-sky imagers in the Optical Mesosphere and Thermosphere Imager system in Japan, located at Rikubetsu (43.5 degrees N, 143.8 degrees E), Shigaraki (34.9 degrees N, 136.1 degrees E), and Sata (31.0 degrees N, 130.7 degrees E). The airglow structures, which were well defined and formed a coherent wave pattern expanding concentrically, were identified over 8 h (2135-2947 LT). We estimate the horizontal wavelength, horizontal phase speed, and wave period as 34.5 km, 50.2 m s(-1), and 11.5 min, respectively. Infrared cloud images from the Geostationary Meteorological Satellite show that the center of the rings estimated from the airglow data corresponds to a spiral band of Typhoon Pongsona (T0226). This unique event provides new insight into coupling between the lower and upper atmosphere.

    DOI: 10.1002/2013GL058087

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  194. Drift velocities of 150-km Field-Aligned Irregularities observed by the Equatorial Atmosphere Radar Reviewed

    Otsuka Yuichi, Mizutani Naruhito, Shiokawa Kazuo, Patra Amit, Yokoyama Tatsuhiro, Yamamoto Mamoru

    Antarctic record   Vol. 57 ( 3 ) page: 369 - 378   2013.11

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    Between 130 and 170 km altitude in the daytime ionosphere, the so-called 150-km field-aligned irregularities (FAIs) have been observed since the 1960s at equatorial regions with several very high frequency (VHF) radars. We report statistical results of 150-km FAI drift velocities on a plane perpendicular to the geomagnetic field, acquired by analyzing the Doppler velocities of 150-km FAIs observed with the Equatorial Atmosphere Radar (EAR) at Kototabang, Indonesia during the period from Aug. 2007 to Oct. 2009. We found that the southward/upward perpendicular drift velocity of the 150-km FAIs tends to decrease in the afternoon and that this feature is consistent with that of F-region plasma drift velocities over the magnetic equator. The zonal component of the 150-km FAI drift velocity is westward and decreases with time, whereas the F-region plasma drift velocity observed with the incoherent scatter radar at Jicamarca, Peru, which is westward, reaches a maximum at about noon. The southward/upward and zonal drift velocities of the 150-km FAIs are smaller than that of the F-region plasma drift velocity by approximately 3 m/s and 25 m/s, respectively, on average. The large difference between the 150-km FAI and F-region plasma drift velocities may not arise from a difference in the magnetic latitudes at which their electric fields are generated. Electric fields generated at the altitude at which the 150-km FAIs occur may not be negligible.

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  195. Comparison of meridional thermospheric winds observed by ionosondes and Fabry-Perot interferometers Reviewed

    Nishioka M., Maruyama T., Otsuka Y., Tsugawa T., Ishibashi H., Shiokawa K., Ishii M.

    Antarctic Record   Vol. 57 ( 3 ) page: 357 - 368   2013.11

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    To comprehend ionospheric-thermospheric coupling, one must understand the thermospheric wind system. However, measuring the thermospheric wind using a Fabry-Perot interferometer (FPI) is not an easy task. Because of this difficulty, some researchers have estimated meridional wind velocities using data obtained from a pair of ionosonde stations near the geomagnetic conjugate points, under the assumption that the meridional wind is the same at the two ionosonde stations (transequatorial mode wind). In this paper, we construct the first comparison of the estimated meridional wind velocities with meridional wind observed with FPIs. We analyzed data from the ionosondes and FPIs installed at Chiang Mai, Thailand, and Kototabang, Indonesia, from 2010. We found that the estimated and observed wind velocities were generally in good agreement on most nights, although on some nights, the wind velocities were different. The assumption that the meridional wind is equal anywhere between the two ionosonde stations would not be suitable for the days when the winds were not in good agreement. We also investigated the seasonal dependence of the correlation between the estimated and observed meridional winds. They were in good agreement from February to April and were not in good agreement from May to July. © 2013 National Institute of Polar Research.

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  196. Drift velocities of 150-km field-aligned irregularities observed by the equatorial atmosphere radar Reviewed

    Otsuka Y.

    Antarctic Record   Vol. 57 ( 3 ) page: 369 - 378   2013.11

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  197. Recent advances in equatorial, low- and mid-latitude aeronomy Preface Reviewed

    Archana Bhattacharyya, Jorge L. Chau, Clezio M. Denardini, David L. Hysell, Jonathan J. Makela, Kazuo Shiokawa, Erhan Kudeki

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 103   page: 1 - 2   2013.10

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    DOI: 10.1016/j.jastp.2013.08.017

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  198. Observation of nighttime medium-scale travelling ionospheric disturbances by two 630-nm airglow imagers near the auroral zone Reviewed

    Shiokawa K., Mori M., Otsuka Y., Oyama S., Nozawa S., Suzuki S., Connors M.

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 103   page: 184-194   2013.10

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    DOI: 10.1016/j.jastp.2013.03.024

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  199. Observation of nighttime medium-scale travelling ionospheric disturbances by two 630-nm airglow imagers near the auroral zone Reviewed

    Shiokawa, K., M. Mori, Y. Otsuka, S. Oyama, S. Nozawa, S. Suzuki, and M. Connors

    Journal of Atmoshere and Solar-Terrestrial Physics   Vol. 103   page: 184-194   2013.9

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  200. Ionogram-based range-time displays for observing relationships between ionosonde satellite traces, spread F and drifting optical plasma depletions Reviewed

    Lynn K. J. W., Otsuka Y., Shiokawa K.

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 98   page: 105-112   2013.6

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    DOI: 10.1016/j.jastp.2013.03.020

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  201. Planetary wave induced wind and airglow oscillations in the middle latitude MLT region Reviewed

    H. Takahashi, K. Shiokawa, F. Egito, Y. Murayama, S. Kawamura, C. M. Wrasse

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 98   page: 97 - 104   2013.6

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    Upper mesosphere airglow emissions and temperature observed at Rikubetsu (43.5 degrees N,143.8 degrees E) and mesospheric winds observed at Wakkanai (45.4 degrees N,141.8 degrees E), Japan, from January to December 2005 were used to analyze periodic oscillations of 2-16 days. During the January to March period and after September, both winds and airglow demonstrated clear 8-, 10- and 16-day oscillations. Downward phase progressions observed in the oscillations indicate that these are a signature of Rossby mode planetary waves. The 16-day wave was more evident in the zonal wind than the meridional. The 10-day wave was observed in January and March, on the basis of only a few cycles superposed on the 16-day wave. Airglow OI 557.7 nm, O-2 and OH(6,2) band emissions and O-2 rotational temperature also showed significant amplitude of oscillation induced by the wave passages. For the 10-day wave, OI557.7 nm showed an amplitude of oscillation equals to or more than 50% of the mean intensity level, O-2 similar to 45% and OH 25%. Large amplitudes of oscillation of the airglow during the passage of planetary waves suggest the possible vertical transport of atomic oxygen in addition to the density and temperature variations intrinsic to the wave events. (C) 2013 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2013.03.014

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  202. Substorm onset and expansion phase intensification precursors seen in polar cap patches and arcs Reviewed

    Y. Nishimura, L. R. Lyons, K. Shiokawa, V. Angelopoulos, E. F. Donovan, S. B. Mende

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 118 ( 5 ) page: 2034 - 2042   2013.5

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    Localized, transient polar cap flows impinging on the poleward boundary of the nightside auroral oval have been suggested to precede poleward boundary intensifications (PBIs), which are often followed by auroral streamers, some of which propagate equatorward and appear to lead to substorm auroral onset. While echo coverage often limits radar flow measurements, imaging of polar cap patches and arcs has the potential to monitor localized polar cap flows by tracing emission structures, previously associated with enhanced flows, over long distances. We use such imaging to examine if polar cap patches and arcs moving over large distances can be seen as possible precursors to presubstorm-onset PBIs. We find evidence that such features, which are longitudinally narrow, propagate from the dayside polar region toward the nightside polar cap boundary prior to pre-onset PBIs. This sequence indicates that transient activity in the dayside polar region may initiate polar cap patches and arcs that propagate across the polar cap and are followed by pre-onset PBIs. Furthermore, we find evidence that expansion-phase active aurora expanded poleward soon after additional polar cap patches and arcs reached close to the nightside polar cap boundary. The expansion phase auroral activity significantly weakened when polar cap patches/arcs disappeared. Our findings suggest that plasma transport originating from the dayside and reaching the nightside open-closed boundary may trigger in plasma sheet flow bursts and play a crucial role in pre- and post-onset auroral activity. Polar cap imaging offers the possibility for monitoring such localized, transient plasma transport over large distances.

    DOI: 10.1002/jgra.50279

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  203. Substorm onset and expansion phase intensification precursors seen in polar cap patches and arcs Reviewed

    Nishimura Y., Lyons L. R., Shiokawa K., Angelopoulos V., Donovan E. F., Mende S. B.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 118 ( 5 ) page: 2034 - 2042   2013.5

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    DOI: 10.1002/jgra.50279

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  204. Substorm onset and expansion phase intensification precursors seen in polar cap patches and arcs Reviewed

    Nishimura Y.

    Journal of Geophysical Research: Space Physics   Vol. 118 ( 5 ) page: 2034 - 2042   2013.5

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    DOI: 10.1002/jgra.50279

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  205. プラズマバブル発生に伴う全電子数変化率の緯度依存性

    鈴木 順也, 中田 裕之, 鷹野 敏明, 津川 卓也, 斉藤 昭則, 大塚 雄一, 塩川 和夫

    大気電気学会誌 = / Society of Atmospheric Electricity of Japan   Vol. 7 ( 1 ) page: 60 - 61   2013.4

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  206. Evidence of gravity wave ducting in the mesopause region from airglow network observations Reviewed

    Suzuki, S, Shiokawa, K, Otsuka, Y, Kawamura, S, Murayama, Y

    GEOPHYSICAL RESEARCH LETTERS   Vol. 40 ( 3 ) page: 601 - 605   2013.2

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    DOI: 10.1029/2012GL054605

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  207. Geomagnetic conjugate observations of plasma-sheet electrons by the FAST and THEMIS satellites Reviewed

    S. Lee, K. Shiokawa, J. P. McFadden, K. Seki

    Journal of Geophysical Research: Space Physics   Vol. 118 ( 1 ) page: 132 - 145   2013.1

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    We investigate pitch-angle distributions and spectral shapes of auroral electrons simultaneously observed during three conjunction events by the FAST satellite at altitudes of 2500-3500 km and by the THEMIS satellite in the plasma sheet at 7-13 RE. All three events were on the lower latitude of the auroral oval. Conjunction event 1 occurred at ~1914:45 UT on 10 April 2008. Electron spectra at energies of 0.1-3 keV are correlated well between the two satellites, while the precipitating electrons above 3 keV are missing at FAST. Event 2 occurred at 1255:26 UT on 26 April 2008. Electron spectra above 3 keV are correlated well between the two satellites. An additional broad spectral peak at energies of 0.1-0.5 keV was observed by FAST. Event 3 occurred at 0058:04 UT on 25 December 2008. Precipitating electrons of 0.5-5 keV obtained by FAST are correlated well with those of THEMIS-C, while a monoenergetic peak at 0.1-0.2 keV was observed only by FAST. For the three conjunction events, we conclude that high-energy precipitating auroral electrons observed by FAST directly come from the equatorial plasma sheet, while low-energy precipitating electrons may come from middle altitudes as a result of acceleration by static potential differences. For missing high-energy (&gt
    3 keV) electrons of event 1, we speculate that the pitch-angle scattering by waves occurs only at a limited energy range. ©2012. American Geophysical Union. All Rights Reserved.

    DOI: 10.1029/2012JA017805

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  208. Ground and satellite observations of low-latitude red auroras at the initial phase of magnetic storms Reviewed

    K. Shiokawa, Y. Miyoshi, P. C. Brandt, D. S. Evans, H. U. Frey, J. Goldstein, K. Yumoto

    Journal of Geophysical Research: Space Physics   Vol. 118 ( 1 ) page: 256 - 270   2013

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    We report ground and satellite observations of unique low-latitude red auroras that appear at the initial phase of geomagnetic storms. For two events on 21 October 2001, and 6 April 2000, the low-latitude red auroras appeared at ∼45° MLAT (L ∼ 2) ∼ 1.5 h after the storm sudden commencement in the postmidnight sector in Japan. Comprehensive satellite data were available for the former event. The energetic neutral atom images obtained by the Imager for Magnetopause-to-Aurora Global Exploration satellite show rapid enhancement of ring current hydrogen and oxygen fluxes at radial distances of ∼ 2-8 RE after the storm sudden commencement and associated with several storm-time substorms. The hydrogen ring-current enhancement occurred particularly in the postmidnight sector where the red aurora was observed. The timing of oxygen flux enhancement associated with a storm-time substorm coincided with the red aurora appearance. This rapid and significant enhancement of energetic neutral atom flux was also confirmed by energetic ion data obtained by the NOAA/POES-16 satellite. Extreme ultraviolet plasmaspheric images obtained by Magnetopause-to-Aurora Global Exploration indicate that the plasmapause was located at L = 2.3-2.5 in the postmidnight sector during the event, indicating that a spatial overlap occurs between the plasmasphere and the enhanced ring current ions at L ∼ 2. Based on these observations, we suggest that large energization of high-energy ring-current ions in the postmidnight inner magnetosphere caused the spatial overlap of these ring-current ions with the low-energy plasmaspheric plasmas at L ∼ 2, producing the low-latitude red auroras at the very beginning of the storms. ©2012. American Geophysical Union. All Rights Reserved.

    DOI: 10.1029/2012JA018001

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  209. GPS observations of medium-scale traveling ionospheric disturbances over Europe Reviewed

    Otsuka, Y, Suzuki, K, Nakagawa, S, Nishioka, M, Shiokawa, K, Tsugawa, T

    ANNALES GEOPHYSICAE   Vol. 31 ( 2 ) page: 163 - 172   2013

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    DOI: 10.5194/angeo-31-163-2013

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  210. Stereoscopic determination of all-sky altitude map of aurora using two ground-based Nikon DSLR cameras Reviewed

    R. Kataoka, Y. Miyoshi, K. Shigematsu, D. Hampton, Y. Mori, T. Kubo, A. Yamashita, M. Tanaka, T. Takahei, T. Nakai, H. Miyahara, K. Shiokawa

    ANNALES GEOPHYSICAE   Vol. 31 ( 9 ) page: 1543 - 1548   2013

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    A new stereoscopic measurement technique is developed to obtain an all-sky altitude map of aurora using two ground-based digital single-lens reflex (DSLR) cameras. Two identical full-color all-sky cameras were set with an 8 km separation across the Chatanika area in Alaska (Poker Flat Research Range and Aurora Borealis Lodge) to find localized emission height with the maximum correlation of the apparent patterns in the localized pixels applying a method of the geographical coordinate transform. It is found that a typical ray structure of discrete aurora shows the broad altitude distribution above 100 km, while a typical patchy structure of pulsating aurora shows the narrow altitude distribution of less than 100 km. Because of its portability and low cost of the DSLR camera systems, the new technique may open a unique opportunity not only for scientists but also for night-sky photographers to complementarily attend the aurora science to potentially form a dense observation network.

    DOI: 10.5194/angeo-31-1543-2013

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  211. Drift velocities of 150-km field-aligned irregularities observed by the equatorial atmosphere radar Reviewed

    Otsuka Y, Mizutani N, Shiokawa K, Patra A, Yokoyama T, Yamamoto M

    Antarctic Record   Vol. 57 ( 3 ) page: 369 - 378   2013

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    DOI: 10.15094/00009711

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    Other Link: http://orcid.org/0000-0001-8392-6455

  212. Substorm onset and expansion phase intensification precursors seen in polar cap patches and arcs Reviewed

    Y. Nishimura, L. R. Lyons, K. Shiokawa, V. Angelopoulos, E. F. Donovan, S. B. Mende

    Journal of Geophysical Research: Space Physics   Vol. 118 ( 5 ) page: 2034 - 2042   2013

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

    Localized, transient polar cap flows impinging on the poleward boundary of the nightside auroral oval have been suggested to precede poleward boundary intensifications (PBIs), which are often followed by auroral streamers, some of which propagate equatorward and appear to lead to substorm auroral onset. While echo coverage often limits radar flow measurements, imaging of polar cap patches and arcs has the potential to monitor localized polar cap flows by tracing emission structures, previously associated with enhanced flows, over long distances. We use such imaging to examine if polar cap patches and arcs moving over large distances can be seen as possible precursors to presubstorm-onset PBIs. We find evidence that such features, which are longitudinally narrow, propagate from the dayside polar region toward the nightside polar cap boundary prior to pre-onset PBIs. This sequence indicates that transient activity in the dayside polar region may initiate polar cap patches and arcs that propagate across the polar cap and are followed by pre-onset PBIs. Furthermore, we find evidence that expansion-phase active aurora expanded poleward soon after additional polar cap patches and arcs reached close to the nightside polar cap boundary. The expansion phase auroral activity significantly weakened when polar cap patches/arcs disappeared. Our findings suggest that plasma transport originating from the dayside and reaching the nightside open-closed boundary may trigger in plasma sheet flow bursts and play a crucial role in pre- and post-onset auroral activity. Polar cap imaging offers the possibility for monitoring such localized, transient plasma transport over large distances. Key Points Polar cap patches and arcs are found to precede pre-onset PBIs.Expansion-phase further intensifications are also preceded by patches and arcs.Dayside region is found important for triggering flow bursts and substorms. ©2013. American Geophysical Union. All Rights Reserved.

    DOI: 10.1002/jgra.50279

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  213. Giant ionospheric disturbances observed with the SuperDARN Hokkaido HF radar and GPS network after the 2011 Tohoku earthquake Reviewed

    Ogawa Tadahiko, Nishitani Nozomu, Tsugawa Takuya, SHIOKAWA Kazuo

    Earth, planets and space   Vol. 64 ( 12 ) page: 1295-1307   2012.12

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  214. Special Issue: Recent Progress in the Vertical Coupling in the Atmosphere-Ionosphere System Preface Reviewed

    Dora Pancheva, Kazuo Shiokawa, Petra Knizova, Weixing Wan

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 90-91 ( 1 ) page: V - VI   2012.12

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    DOI: 10.1016/j.jastp.2012.10.002

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  215. VHF radar observations of post-midnight f-region field-aligned irregularities over indonesia during solar minimum Reviewed

    Otsuka Y., Shiokawa K., Nishioka M., Effendy

    Indian Journal of Radio and Space Physics   Vol. 41 ( 2 ) page: 199 - 207   2012.12

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    A VHF backscatter radar with operating frequency 30.8 MHz has been operated at Kototabang (0.20°S, 100.32°E; dip latitude 10.4°S), Indonesia since February 2006. The F-region field-aligned irregularities (FAIs) observed by this radar from February 2006 to December 2010 during a solar minimum period have been analyzed and found that FAIs appeared frequently at the post-midnight sector between May and August every year from 2006 to 2010. Five-beam measurements by the radar revealed zonal propagation of the F-region FAIs. The present paper reports, for the first time, statistics of the zonal propagation velocity of the post-midnight FAIs. Between May and August, 46% (14%) of the post-midnight FAIs propagated westward (eastward), and zonal propagation was not discernible for 40% of the post-midnight FAIs. Average velocity was approximately 50 m s-1 westward. The post-midnight FAIs were likely associated with either plasma bubbles or medium-scale traveling ionospheric disturbances (MSTIDs).

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  216. Development of low-cost sky-scanning Fabry-Perot interferometers for airglow and auroral studies Reviewed

    Shiokawa, K., Y. Otsuka, S. Oyama, S. Nozawa, M. Satoh, Y. Katoh, Y. Hamaguchi, Y. Yamamoto and J. Meriwether

    Earth Planets and Space   Vol. 64 ( 11 ) page: 1033-1046   2012.11

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  217. Reflection height of daytime tweek atmospherics during the solar eclipse of 22 July 2009 Reviewed

    Hiroyo Ohya, Fuminori Tsuchiya, Hiroyuki Nakata, Kazuo Shiokawa, Yoshizumi Miyoshi, Kozo Yamashita, Yukihiro Takahashi

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117 ( 11 )   2012.11

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    We report multipoint observations of daytime tweek atmospherics during the solar eclipse of 22 July 2009. Sixteen and sixty-three tweek atmospherics were observed at Moshiri and Kagoshima, Japan, where the magnitudes of the solar eclipse were 0.458 and 0.966, respectively. This was the first observation of tweek atmospherics during a low-magnitude eclipse (0.458). The average and standard deviation of the reflection height were 94.9 +/- 13.7 km at Moshiri and 87.2 +/- 12.9 km at Kagoshima. The reflection height at Moshiri was almost the same as that for normal nighttime conditions in July (96.7 +/- 12.6 km) in spite of the low magnitude of the eclipse. The reflection height at Kagoshima seems be divided into two parts: propagation across the total solar eclipse path and propagation in the partial solar eclipse path. During the eclipse, we also observed the phase variation in the LF transmitter signals. The average change in the phase delay of the LF signals was 109 degrees for the paths that crossed the eclipse path and 27 degrees for the paths that did not cross the eclipse path. Assuming a normal daytime height for LF waves of 65 km, a ray tracing analysis indicates that the variations in phase correspond to a height increase of 5-6 km for the paths across the eclipse and 1-2 km for partial eclipse paths. The wide range of estimated tweek reflection heights at Kagoshima also suggests a difference in electron density in the lower ionosphere between total and partial solar eclipses.

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  218. Development of low-cost sky-scanning Fabry-Perot interferometers for airglow and auroral studies Reviewed

    Shiokawa K., Otsuka Y., Oyama S., NOZAWA S., SATOH M., KATOH Y., HAMAGUCHI Y., YAMAMOTO Y., MERIWETHER J.

    Earth, planets and space   Vol. 64 ( 11 ) page: 1033-1046   2012.11

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  219. Observation of equatorial nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow images over 7 years Reviewed

    D. Fukushima, K. Shiokawa, Y. Otsuka, T. Ogawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117 ( 10 )   2012.10

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    We report on nighttime medium- scale traveling ionospheric disturbances (MSTIDs) observed at Kototabang, Indonesia (geographic longitude: 100.3 degrees E; geographic latitude: 0.2 degrees S; and geomagnetic latitude: 10.6 degrees S) during a 7-year period from October 2002 to October 2009. MSTIDs were observed in 630-nm nighttime airglow images by using a highly sensitive all-sky airglow imager at Kototabang. The averages and standard deviations of horizontal phase velocity, period, and horizontal wavelength of MSTIDs observed during the 7 years were 320 +/- 170 m/s, 42 +/- 11 min, and 790 +/- 440 km, respectively. The occurrence rate of the observed MSTIDs decreased with decreasing solar activity. The average horizontal wavelength of MSTIDs increased with decreasing solar activity. Southward MSTIDs were dominant throughout the 7 years of observations. These facts are consistent with the hypothesis that the observed MSTIDs are caused by gravity waves in the thermosphere. Moreover, we compared the propagation directions of the observed MSTIDs with the locations of tropospheric convection activity for the events where gravity waves producing the observed MSTIDs could have existed in the lower atmosphere. Strong tropospheric convection was found within +/- 30 degrees from the source directions of MSTIDs in 81% of the MSTID events. In such events, gravity waves were possibly generated from deep convection in the troposphere and directly propagated into the thermosphere.

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  220. Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening Reviewed

    Shiokawa, K, Mori, M, Otsuka, Y, Oyama, S, Nozawa, S

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117 ( 10 )   2012.10

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    We report for the first time the rapid oscillating motion of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) based on airglow imaging observations at Tromso (magnetic latitude: 67.1 degrees N), Norway on 8 December, 2009. The MSTIDs appeared in 630-nm airglow images at 1530 UT as wave-like structures south of Tromso with a horizontal wavelength of similar to 200 km and a phase surface of north to south. They moved eastward with velocities of 30-60 m/s. The velocity was faster in the poleward-side of the MSTIDs, forming a northeast-southwest phase surface at later times. This phase surface direction is opposite to that of midlatitude MSTIDs. The MSTIDs show sudden oscillations and phase jump in the east-west direction with a timescale of similar to 10 min at 1730 UT. The oscillations were associated with an auroral brightening observed at the poleward edge of the images and small magnetic field perturbations observed by ground magnetometers. The Doppler measurement of the 630-nm airglow by a Fabry-Perot interferometer at Tromso showed a stable southeastward thermospheric wind with a velocity of similar to 150 m/s. These observations indicate that the MSTID oscillations were linked to auroral electric field in the ionosphere, implying that the observed MSTIDs are ionospheric plasma structures. We suggest that the observed MSTIDs were created by atmospheric gravity waves at the beginning, left as fossil plasma structures even after the gravity wave packet dissipated in the thermosphere, moved eastward according to the background electric field driven by the F-region dynamo, and oscillated associated with the auroral electric field.

    DOI: 10.1029/2012JA017928

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  221. Magnetospheric responses to the passage of the interplanetary shock on 24 November 2008 Reviewed

    K-H Kim, D-H Lee, K. Shiokawa, E. Lee, J-S Park, H-J Kwon, V. Angelopoulos, Y-D. Park, J. Hwang, N. Nishitani, T. Hori, K. Koga, T. Obara, K. Yumoto, D. G. Baishev

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.10

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    The passage of an interplanetary (IP) shock was detected by Wind, ACE, Geotail, and THEMIS-B in the solar wind on 24 November 2008. From the propagation time of the IP shock at the spacecraft, it is expected that the IP shock front is aligned with the Parker spiral and strikes the postnoon dayside magnetopause first. Using multipoint observations of the sudden commencement (SC) at THEMIS probes, GOES 11, and ETS in the dayside magnetosphere, we confirmed that the magnetospheric response to the IP shock starts earlier in the postnoon sector than in the prenoon sector. We found that the estimated normal direction of the SC front is nearly aligned with the estimated IP shock normal. We also found that the SC front normal speed is much slower than the fast mode speed and is about 22-56% of the IP shock speed traveling in the solar wind. Thus, we suggest that the major field changes of the SC in the dayside magnetosphere are not due to the magnetic flux carried by hydromagnetic waves but to the increased solar wind dynamic pressure behind the shock front sweeping the magnetopause. The SC event appears as a step-like increase in the H component at the low-latitude Bohyun station and a negative-then-positive variation in the H component at the high-latitude Chokurdakh (CHD) station in the morning sector. During the negative perturbation at CHD, the SuperDARN Hokkaido radar detected a downward motion in the ionosphere, implying westward electric field enhancement. Using the THEMIS electric field data, it is confirmed that the westward electric field corresponds to the inward plasma motion in the dayside magnetosphere due to the magnetospheric compression.

    DOI: 10.1029/2012JA017871

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  222. Visualization of ion cyclotron wave and particle interactions in the inner magnetosphere via THEMIS-ASI observations Reviewed

    K. Sakaguchi, Y. Miyoshi, E. Spanswick, E. Donovan, I. R. Mann, V. Jordanova, K. Shiokawa, M. Connors, J. C. Green

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.10

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    Interaction with EMIC (electromagnetic ion cyclotron) waves is thought to be a key component contributing to the very rapid loss of both ring current and radiation belt particles into the atmosphere. Estimated loss rates are heavily dependent on the assumed spatial distribution of the EMIC wave. Statistical maps of the spatial distribution have been produced using in-situ satellite data. However, with limited satellite data it is impossible to deduce the true spatial distribution. In this study, we present ground-based observations using all-sky imager and search coil magnetometer networks, which provide the large-scale distribution and motion of the EMIC wave-particle interaction regions. We observed several spots of isolated proton auroras simultaneously with Pc1/EMIC waves at subauroral latitudes during the expansion phase of a storm-time substorm on 9 March 2008. The isolated auroras were distributed over similar to 4-hours MLT preceding midnight. The POES-17 satellite confirmed enhancements of 30-keV proton precipitations over the isolated auroras. The equatorward motion of the auroras and frequency drift of the wave were consistent with the plasmasphere eroding due to a polar cap potential enhancement modeled by a numerical simulation. We also found that relativistic electron precipitation was not always associated with the isolated aurora, depending strongly on the plasma density profile near the plasmapause. This study shows that the specific distribution of ring current proton precipitation can be visualized through the ground network observations. By combining with upcoming inner-magnetosphere satellite missions, these remote-sensing observations are very important for quantitative understanding of the particle loss in the inner magnetosphere.

    DOI: 10.1029/2012JA018180

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  223. Space-time variability of polar cap patches: Direct evidence for internal plasma structuring Reviewed

    Dahlgren H., Perry G. W., Semeter J. L., St-Maurice J. -P., Hosokawa K., Nicolls M. J., Greffen M., Shiokawa K., Heinselman C.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.9

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    DOI: 10.1029/2012JA017961

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  224. Space-time variability of polar cap patches: Direct evidence for internal plasma structuring Reviewed

    H. Dahlgren, G. W. Perry, J. L. Semeter, J. -P. St-Maurice, K. Hosokawa, M. J. Nicolls, M. Greffen, K. Shiokawa, C. Heinselman

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.9

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    Coordinated observations of ionospheric variability near the geomagnetic pole using the Resolute Bay Incoherent Scatter Radar (RISR-N), Super Dual Auroral Radar Network (SuperDARN) High Frequency (HF) radars, and all-sky imagers have clarified the relative contribution of structuring mechanisms operating on polar plasma patches. From the multipoint RISR-N observations, a three dimensional image can be constructed of the plasma parameters. The colocated coherent echoes from the SuperDARN radars provide information on field aligned irregularities, and from all-sky imagers located in Resolute Bay, Canada and Qaanaaq, Greenland, information is obtained on the emission brightness at different wavelengths. A good correlation is found between the location of the coherent, incoherent and optical signals of patches. From the SuperDARN radar data it is evident that plasma irregularities seem to be present throughout the region of enhanced electron density. The patches are observed to be formed in the cusp region due to bursty flux transfer events and are then transported across the polar cap. During the time period of about 10 minutes when a patch drifted through the RISR-N field of view, the patch seemed to undergo significant deformation in all three spatial dimensions, with density fluctuations of about 10% and spatial variations leading to stretching and tilting of the patch. The findings show that plasma structuring can likely occur within polar cap patches, which support previous suggestions that a patch is highly variable as it drifts across the polar cap, with a faster spread of irregularities throughout the patch as a result.

    DOI: 10.1029/2012JA017961

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  225. Observed correlation between pulsating aurora and chorus waves at Syowa Station in Antarctica: a case study Reviewed

    Ozaki, M, S. Yagitani, K. Ishizaka, K. Shiokawa, Y. Miyoshi, A. Kadokura, H. Yamagishi, R. Kataoka, A. Ieda, Y. Ebihara, N. Sato, I. Nagano

    J. Geophys. Res.   Vol. 117 ( 8 ) page: 8211 - 8211   2012.8

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    A high correlation between a pulsating auroral patch and grouped chorus waves was observed on 17 April 2006 at Syowa Station in Antarctica. The spatial distribution of aurora-chorus correlation coefficients is evaluated in order to determine the source region. A pulsating patch at the highest-correlation pixel shows a one-to-one correspondence with the intensity variation of the grouped chorus waves, consisting of successive rising-tone elements with a duration and spacing of 2-3 s and 20-30 s, respectively. The generation region of the chorus waves is estimated from the latitude and longitude dependence of the equatorial electron gyrofrequencies using the IGRF geomagnetic field model. The extent of the estimated latitude and longitude is consistent with the spatial distribution of the high-correlation aurora-chorus region. The time difference between the chorus waves and the scattered electrons is also evaluated to discuss the validity of the source region. It shows that electrons reached the ionosphere sooner than the associated chorus waves by similar to 1 s, consistent with the theoretical value for conjugate pulsating aurora generated at the equator. These results support the hypothesis that pulsating aurora is caused by pitch angle scattering of high-energy electrons by whistler mode chorus waves, via a cyclotron resonance at the equator. These results are the first ground-based observations of high correlations between a spatially extended aurora and chorus waves.

    DOI: 10.1029/2011JA017478

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  226. On post-midnight field-aligned irregularities observed with a 30.8-MHz radar at a low latitude: Comparison with F-layer altitude near the geomagnetic equator Reviewed

    M. Nishioka, Y. Otsuka, K. Shiokawa, T. Tsugawa, Effendy, P. Supnithi, T. Nagatsuma, K. T. Murata

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.8

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    We investigated the relationship between post-midnight F-region field aligned irregularities (FAIs) and F-layer altitude by analyzing data of a 30.8-MHz radar installed 5at Kototabang, Indonesia (0.2 degrees S, 100.3 degrees E; geomagnetic latitude 10.4 degrees S) and an ionosonde installed at Chumphon, Thailand (10.7 degrees N, 99.4 degrees E; geomagnetic latitude 3.3 degrees N). Chumphon is located near the geomagnetic equator on approximately the same meridian as Kototabang. Case studies show that the altitude of the F-layer rose at Chumphon a half hour before the post-midnight FAIs appeared at Kototabang. The Doppler velocity of the E-region FAIs observed simultaneously by the 30.8-MHz radar was downward, indicating that the F-layer uplift was not caused by the electric field. We also investigated seasonal variations of the post-midnight FAI occurrence and the F-layer altitude. Both the post-midnight FAIs and the uplift of the F-layer were frequently seen around midnight between May and August. The seasonal variation of the midnight F-layer uplift around the geomagnetic equator coincided with that of the post-midnight FAI occurrence at Kototabang. These results suggest that the uplift of the F-layer would play an important role in the generation of post-midnight FAIs. We evaluated the linear growth rate of the Rayleigh-Taylor instability based on the altitude of the F-layer observed at Chumphon. The result shows that the uplift of the F-layer can enhance the growth rate because gravity-driven eastward electric current increases. Therefore, we interpret that the observed FAIs were accompanied by plasma bubble, the growth rate of which was reinforced by the uplifted F-layer.

    DOI: 10.1029/2012JA017692

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  227. Disappearance of equatorial plasma bubble after interaction with mid-latitude medium-scale traveling ionospheric disturbance Reviewed

    Otsuka, Y, Shiokawa, K, Ogawa, T

    GEOPHYSICAL RESEARCH LETTERS   Vol. 39 ( 14 )   2012.7

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    DOI: 10.1029/2012GL052286

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  228. GPS total electron content variations associated with poleward moving Sun-aligned arcs Reviewed

    Jayachandran P. T., Hosokawa K., Shiokawa K., Otsuka Y., Watson C., Mushini S. C., MacDougall J. W., Prikryl P., Chadwick R., Kelly T. D.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.5

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    DOI: 10.1029/2011JA017423

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  229. GPS total electron content variations associated with poleward moving Sun-aligned arcs Reviewed

    P. T. Jayachandran, K. Hosokawa, K. Shiokawa, Y. Otsuka, C. Watson, S. C. Mushini, J. W. MacDougall, P. Prikryl, R. Chadwick, T. D. Kelly

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.5

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    GPS total electron content (TEC) has shown quasiperiodic oscillations of varying amplitude associated with poleward moving Sun-aligned arcs. The amplitude of TEC variations showed a maximum of similar to 3 TECU and seemed to decrease as the arcs moved poleward from the source/generation region. Simultaneous DMSP data showed that fluctuations in TEC and optical intensification were caused by precipitation of high-energy (&gt;500 eV) particles. Concurrent ionosonde observations also exhibited quasiperiodic variations (within limit of the resolution of the data) in peak ionospheric electron density of the ionosphere. Bottom height of the ionospheric layers produced by precipitating particles varied between 130 km (upper E region) and 300 km (F region), indicating variable particle precipitation energy. Frequency analysis of high-resolution TEC data showed a broad range of discrete frequency components from 1.60 mHz to 22.80 mHz present in the TEC oscillations, which may provide insight into the energization/modulation of precipitating particles by these oscillations. A broad distribution of equivalent vertical thickness of arcs was calculated using GPS TEC and ionosonde measurements of peak electron density. This distribution showed a minimum thickness of 21 km, a maximum of 84 km, and an average of 49 km. The equivalent vertical thickness also showed a linear relationship with bottomside height of the ionospheric layer (auroral arc). The relationship showed an increase in the vertical thickness with an increase in bottomside height of the layer. This relationship is a consequence of variations in the energy of the precipitating particles causing different ionospheric production profiles.

    DOI: 10.1029/2011JA017423

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  230. Direct three-dimensional imaging of polar ionospheric structures with the Resolute Bay Incoherent Scatter Radar Reviewed

    H. Dahlgren, J. L. Semeter, K. Hosokawa, M. J. Nicolls, T. W. Butler, M. G. Johnsen, K. Shiokawa, C. Heinselman

    GEOPHYSICAL RESEARCH LETTERS   Vol. 39 ( 5 )   2012.3

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    Ionospheric plasma density structures in the dayside F-region of the polar cap are commonly occurring events, but adequate measurements of their formation and evolution have been sparse. With the advent of the advanced modular incoherent scatter radar RISR-N (Resolute Bay Incoherent Scatter Radar) it is now possible for the first time to study the temporal evolution of the plasma properties in the polar cap region in three dimensions, with a spatial resolution of tens of kilometers, from which the plasma rest frame can be experimentally established. We demonstrate the strength of the diagnostic with observations from an event of enhanced plasma density observed over Resolute Bay in December 2009. A colocated all-sky imager showed faint 630.0 and 557.7 nm emission corresponding to the plasma enhancements, and the structures could be traced back to a formation region in the open/closed field line boundary. This new plasma imaging technique will provide important information on the mechanisms controlling the structuring in the high latitude ionosphere. Citation: Dahlgren, H., J. L. Semeter, K. Hosokawa, M. J. Nicolls, T. W. Butler, M. G. Johnsen, K. Shiokawa, and C. Heinselman (2012), Direct three-dimensional imaging of polar ionospheric structures with the Resolute Bay Incoherent Scatter Radar, Geophys. Res. Lett., 39, L05104, doi:10.1029/2012GL050895.

    DOI: 10.1029/2012GL050895

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  231. Electron and wave characteristics observed by the THEMIS satellites near the magnetic equator during a pulsating aurora Reviewed

    A. Nakajima, K. Shiokawa, K. Sakaguchi, Y. Miyoshi, S. Lee, V. Angelopoulos, O. Le Contel, J. P. McFadden, J. W. Bonnell, K. -H. Fornacon, E. Donovan

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.3

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    Based on conjugate ground and THEMIS satellite observations, we show electron spectra and wave characteristics near the magnetic equatorial plane during a pulsating aurora event on the high latitude side of the auroral oval. The pulsating aurora was observed by a 30-Hz sampled all-sky imager (ASI) at Gillam (56.4 degrees N, 265.4 degrees E), Canada, at similar to 0840-0910 UT on 8 January 2008. The auroral intensity pulsation at the possible THEMIS D (THD) footprints had frequency peaks at similar to 0.1-0.2 Hz. The footprint of THD was in the poleward part of the proton aurora observed by a meridian-scanning photometer. After auroral pulsation began at similar to 0842 UT, both THD and THEMIS E which was near THD in the mid-tail at 11.6-11.8 R-E, observed enhanced field-aligned electron fluxes at energies of 1-10 keV. However, the amplitudes of whistler mode waves and electrostatic cyclotron harmonics (ECH) waves observed by THD with the highest sampling rate of 8 kHz were not significant, showing a marked contrast to the recent report of clear correlation between whistler mode waves and auroral pulsations observed at 5-9 R-E. We suggest that the observed field-aligned electrons, which are probably caused by Fermi-type acceleration associated with earthward plasma flow in the mid-tail plasma sheet, are modulated by some wave processes to cause pulsating auroras.

    DOI: 10.1029/2011JA017066

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  232. Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes Reviewed

    Nomura R., Shiokawa K., Sakaguchi K., Otsuka Y., Connors M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.2

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    DOI: 10.1029/2011JA017241

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  233. Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes Reviewed

    R. Nomura, K. Shiokawa, K. Sakaguchi, Y. Otsuka, M. Connors

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 117   2012.2

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    We have investigated the polarization of Pc1 geomagnetic pulsations and related proton auroras at subauroral latitudes, using an induction magnetometer and an all-sky camera at Athabasca, Canada (54.7 degrees N, 246.7 degrees E, magnetic latitude (mlat) 61.7 degrees N). Isolated proton auroras often appear in association with Pc1 pulsations, because of proton scattering by electromagnetic ion cyclotron (EMIC) waves in the magnetosphere. We used the proton aurora as a proxy for the location and size of the Pc1 ionospheric source. For 27 Pc1 events with simultaneously observed proton auroras over 4 years from September 7, 2005 to September 6, 2009, we calculated the distances between the Pc1 ionospheric source and the observation site, normalized by the scale size of the source. We tried three different definitions of the scale size of Pc1 ionospheric source to calculate the normalized distances. We found that the rotation angle theta between the Pc1 polarization ellipse and the direction to the proton aurora changes from 90 degrees to 0 degrees as the normalized distance increases. For the definition of the scale sizes that gives most clear theta-transition from 90 degrees to 0 degrees, the transition occurs at the normalized distance similar to 2.0-4.0, while it was similar to 1.0-2.0 by the model calculation of Fujita and Tamao (1988). The averaged major axes tend to point toward the proton aurora at larger distances. The difference of the transition location may imply that the Pc1 ionospheric sources are larger than the isolated proton auroras, or that the inhomogenuity of the ionospheric conductivity by the proton precipitation affects the transition distances.

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  234. Giant ionospheric disturbances observed with the SuperDARN Hokkaido HF radar and GPS network after the 2011 Tohoku earthquake Reviewed

    Ogawa Tadahiko, Nishitani Nozomu, Tsugawa Takuya, Shiokawa Kazuo

    EARTH PLANETS AND SPACE   Vol. 64 ( 12 ) page: 1295-1307   2012

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    DOI: 10.5047/eps.2012.08.001

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  235. Development of low-cost sky-scanning Fabry-Perot interferometers for airglow and auroral studies Reviewed

    K. Shiokawa, Y. Otsuka, S. Oyama, S. Nozawa, M. Satoh, Y. Katoh, Y. Hamaguchi, Y. Yamamoto, J. Meriwether

    EARTH PLANETS AND SPACE   Vol. 64 ( 11 ) page: 1033 - 1046   2012

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    We have developed new Fabry-Perot interferometers (FPIs) that are designed to measure thermospheric winds and temperatures as well as mesospheric winds through the airglow/aurora emissions at wavelengths of 630.0 nm and 557.7 nm, respectively. One FPI (FP01), possessing a large aperture etalon (diameter: 116 mm), was installed at the EISCAT Tromso site in 2009. The other FPIs, using 70-mm diameter etalons, were installed in Thailand, Indonesia, and Australia in 2010-2011 (FP02-FP04) by the Solar-Terrestrial Environment Laboratory, and in Peru (Nazca and Jicamarca) and Alaska (Poker Flat) by Clemson University. The FPIs with 70-mm etalons are low-cost compact instruments, suitable for multipoint network observations. All of these FPIs use low-noise cooled-CCD detectors with 1024 x 1024 pixels combined with a 4-stage thermoelectric cooling system that can cool the CCD temperature down to -80 degrees C. The large incident angle (maximum: 1.3 degrees-1.4 degrees) to the etalon achieved by the use of multiple orders increases the throughput of the FPIs. The airglow and aurora observations at Tromso by FP01 show wind velocities with typical random errors ranging from 2 to 13 m s(-1) and from 4 to 27 m s(-1) for mesosphere (557.7 nm) and thermosphere (630.0 nm) measurements, respectively. The 630.0-nm airglow observations at Shigaraki, Japan, by FP02-FP04 and by the American FPI instruments give thermospheric wind velocities with typical random errors that vary from 2 m s(-1) to more than 50 m s(-1) depending on airglow intensity.

    DOI: 10.5047/eps.2012.05.004

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  236. Signatures of moving polar cap arcs in the F-region PolarDARN echoes Reviewed

    A. V. Koustov, K. Hosokawa, N. Nishitani, K. Shiokawa, H. Liu

    ANNALES GEOPHYSICAE   Vol. 30 ( 3 ) page: 441 - 455   2012

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    Joint observations of the all-sky camera at Resolute Bay (Nunavut, Canada) and the Polar Dual Auroral Radar Network (PolarDARN) HF radars at Rankin Inlet and Inuvik (Canada) are considered to establish radar signatures of poleward moving polar cap arcs 'detaching' from the auroral oval. Common features of the events considered are enhanced power or echo occurrence in the wake of the arcs and enhanced spectral width of these echoes. When the arcs were oriented along some of the radar beams, velocity reversals at the arc location were observed with the directions of the arc-associated flows corresponding to a converging electric field. For the event of 9 December 2007, two arcs were poleward progressing almost along the central beams of the Inuvik radar at the speed close to the &lt; B &gt; E &lt;/B &gt; x &lt; B &gt; B &lt;/B &gt; drift of the bulk of the F-region plasma as inferred from HF Doppler velocities and from independent measurements by the Resolute Bay ionosonde. In global-scale convection maps inferred from all Super Dual Auroral Radar Network (SuperDARN) radar measurements, the polar cap arcs were often seen close to the reversal line of additional mesoscale convection cells located poleward of the normal cells related to the auroral oval.

    DOI: 10.5194/angeo-30-441-2012

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  237. The Energization and Radiation in Geospace (ERG) Project Reviewed

    Y. Miyoshi, T. Ono, T. Takashima, K. Asamura, M. Hirahara, Y. Kasaba, A. Matsuoka, H. Kojima, K. Shiokawa, K. Seki, M. Fujimoto, T. Nagatsuma, C. Z. Cheng, Y. Kazama, S. Kasahara, T. Mitani, H. Matsumoto, N. Higashio, A. Kumamoto, S. Yagitani, Y. Kasahara, K. Ishisaka, L. Blomberg, A. Fujimoto, Y. Katoh, Y. Ebihara, Y. Omura, M. Nose, T. Hori, Y. Miyashita, Y. -M. Tanaka, T. Segawa

    DYNAMICS OF THE EARTH'S RADIATION BELTS AND INNER MAGNETOSPHERE   Vol. 199   page: 103 - 116   2012

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    The Energization and Radiation in Geospace (ERG) project for solar cycle 24 will explore how relativistic electrons in the radiation belts are generated during space stout's. This geospace exploration project consists of three research teams: the ERG satellite observation team, the ground-based network observation team, and the integrated data analysis/simulation team. Satellite observation will provide in situ measurements of features such as the plasma distribution function, electric and magnetic fields, and plasma waves, whereas remote sensing by ground-based observations using, for example, HF radars, magnetometers, optical instruments, and radio wave receivers will provide the global state of the geospace. Various kinds of data will be integrated and compared with numerical simulations for quantitative understanding. Such a synergetic approach is essential for comprehensive understanding of relativistic electron generation/loss processes through cross-energy and cross-regional coupling in which different plasma populations and regions are dynamically coupled with each other. In addition, the ERG satellite will utilize a new and innovative measurement technique for wave-particle interactions that can directly measure the energy exchange process between particles and plasma waves. In this paper, we briefly review some of the profound problems regarding relativistic electron accelerations and losses that will be solved by the ERG project, and we provide an overview of the project.

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  238. Auroral Signatures of the Dynamic Plasma Sheet Reviewed

    A. Keiling, K. Shiokawa, V. Uritsky, V. Sergeev, E. Zesta, L. Kepko, N. Ostgaard

    AURORAL PHENOMENOLOGY AND MAGNETOSPHERIC PROCESSES: EARTH AND OTHER PLANETS   Vol. 197   page: 317 - 335   2012

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    Understanding the physical connections of the coupled magnetosphere-ionosphere system will result in a more complete explanation of the aurora and will further the goal of being able to interpret the global auroral distributions as a dynamic map of the magnetosphere. Significant advances have been made in recent years toward this goal. In this chapter, we briefly review, while focusing on recent observations, selected auroral phenomena that are driven by magnetospheric processes. These include expansion of substorm aurora, plasma sheet waves and auroral modulations, ballooning instability and auroral beads, dipolarization/plasma injections and the auroral bulge, poleward boundary intensifications and auroral streamers, vortical flows and auroral spirals, and plasma flows prior to auroral onset. In addition, other auroral phenomena, such as auroral arcs, diffuse auroras, auroral asymmetry/conjugacy in the conjugate hemispheres, and auroral magneto spheric currents, are highlighted here but expanded in other chapters of this monograph for in-depth reviews.

    DOI: 10.1029/2012GM001231

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  239. Electron and wave characteristics observed by the THEMIS satellites near the magnetic equator during a pulsating aurora Reviewed

    A. Nakajima, K. Shiokawa, K. Sakaguchi, Y. Miyoshi, S. Lee, V. Angelopoulos, O. Le Contel, J. P. McFadden, J. W. Bonnell, K. H. Fornacon, E. Donovan

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 3 )   2012

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    Based on conjugate ground and THEMIS satellite observations, we show electron spectra and wave characteristics near the magnetic equatorial plane during a pulsating aurora event on the high latitude side of the auroral oval. The pulsating aurora was observed by a 30-Hz sampled all-sky imager (ASI) at Gillam (56.4°N, 265.4°E), Canada, at ∼0840-0910 UT on 8 January 2008. The auroral intensity pulsation at the possible THEMIS D (THD) footprints had frequency peaks at ∼0.1-0.2 Hz. The footprint of THD was in the poleward part of the proton aurora observed by a meridian-scanning photometer. After auroral pulsation began at ∼0842 UT, both THD and THEMIS E which was near THD in the mid-tail at 11.6-11.8 RE, observed enhanced field-aligned electron fluxes at energies of 1-10 keV. However, the amplitudes of whistler mode waves and electrostatic cyclotron harmonics (ECH) waves observed by THD with the highest sampling rate of 8 kHz were not significant, showing a marked contrast to the recent report of clear correlation between whistler mode waves and auroral pulsations observed at 5-9 RE. We suggest that the observed field-aligned electrons, which are probably caused by Fermi-type acceleration associated with earthward plasma flow in the mid-tail plasma sheet, are modulated by some wave processes to cause pulsating auroras. Copyright 2012 by the American Geophysical Union.

    DOI: 10.1029/2011JA017066

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  240. GPS total electron content variations associated with poleward moving Sun-aligned arcs Reviewed

    P. T. Jayachandran, K. Hosokawa, K. Shiokawa, Y. Otsuka, C. Watson, S. C. Mushini, J. W. MacDougall, P. Prikryl, R. Chadwick, T. D. Kelly

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 5 )   2012

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    GPS total electron content (TEC) has shown quasiperiodic oscillations of varying amplitude associated with poleward moving Sun-aligned arcs. The amplitude of TEC variations showed a maximum of ∼3 TECU and seemed to decrease as the arcs moved poleward from the source/generation region. Simultaneous DMSP data showed that fluctuations in TEC and optical intensification were caused by precipitation of high-energy (&gt
    500 eV) particles. Concurrent ionosonde observations also exhibited quasiperiodic variations (within limit of the resolution of the data) in peak ionospheric electron density of the ionosphere. Bottom height of the ionospheric layers produced by precipitating particles varied between 130km (upper E region) and 300km (F region), indicating variable particle precipitation energy. Frequency analysis of high-resolution TEC data showed a broad range of discrete frequency components from 1.60 mHz to 22.80 mHz present in the TEC oscillations, which may provide insight into the energization/modulation of precipitating particles by these oscillations. A broad distribution of equivalent vertical thickness of arcs was calculated using GPS TEC and ionosonde measurements of peak electron density. This distribution showed a minimum thickness of 21km, a maximum of 84km, and an average of 49km. The equivalent vertical thickness also showed a linear relationship with bottomside height of the ionospheric layer (auroral arc). The relationship showed an increase in the vertical thickness with an increase in bottomside height of the layer. This relationship is a consequence of variations in the energy of the precipitating particles causing different ionospheric production profiles. Copyright 2012 by the American Geophysical Union.

    DOI: 10.1029/2011JA017423

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  241. GPS total electron content variations associated with poleward moving Sun-aligned arcs Reviewed

    Jayachandran P.T.

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 5 )   2012

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    DOI: 10.1029/2011JA017423

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  242. Electron and wave characteristics observed by the THEMIS satellites near the magnetic equator during a pulsating aurora Reviewed

    Nakajima A.

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 3 )   2012

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    DOI: 10.1029/2011JA017066

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  243. Magnetospheric responses to the passage of the interplanetary shock on 24 November 2008 Reviewed

    K. H. Kim, D. H. Lee, K. Shiokawa, E. Lee, J. S. Park, H. J. Kwon, V. Angelopoulos, Y. D. Park, J. Hwang, N. Nishitani, T. Hori, K. Koga, T. Obara, K. Yumoto, D. G. Baishev

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 10 )   2012

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    The passage of an interplanetary (IP) shock was detected by Wind, ACE, Geotail, and THEMIS-B in the solar wind on 24 November 2008. From the propagation time of the IP shock at the spacecraft, it is expected that the IP shock front is aligned with the Parker spiral and strikes the postnoon dayside magnetopause first. Using multipoint observations of the sudden commencement (SC) at THEMIS probes, GOES 11, and ETS in the dayside magnetosphere, we confirmed that the magnetospheric response to the IP shock starts earlier in the postnoon sector than in the prenoon sector. We found that the estimated normal direction of the SC front is nearly aligned with the estimated IP shock normal. We also found that the SC front normal speed is much slower than the fast mode speed and is about 22-56% of the IP shock speed traveling in the solar wind. Thus, we suggest that the major field changes of the SC in the dayside magnetosphere are not due to the magnetic flux carried by hydromagnetic waves but to the increased solar wind dynamic pressure behind the shock front sweeping the magnetopause. The SC event appears as a step-like increase in the H component at the low-latitude Bohyun station and a negative-then-positive variation in the H component at the high-latitude Chokurdakh (CHD) station in the morning sector. During the negative perturbation at CHD, the SuperDARN Hokkaido radar detected a downward motion in the ionosphere, implying westward electric field enhancement. Using the THEMIS electric field data, it is confirmed that the westward electric field corresponds to the inward plasma motion in the dayside magnetosphere due to the magnetospheric compression. ©2012. American Geophysical Union. All Rights Reserved.

    DOI: 10.1029/2012JA017871

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  244. Space-time variability of polar cap patches: Direct evidence for internal plasma structuring Reviewed

    H. Dahlgren, G. W. Perry, J. L. Semeter, J. P. St.-Maurice, K. Hosokawa, M. J. Nicolls, M. Greffen, K. Shiokawa, C. Heinselman

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 9 )   2012

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    Coordinated observations of ionospheric variability near the geomagnetic pole using the Resolute Bay Incoherent Scatter Radar (RISR-N), Super Dual Auroral Radar Network (SuperDARN) High Frequency (HF) radars, and all-sky imagers have clarified the relative contribution of structuring mechanisms operating on polar plasma patches. From the multipoint RISR-N observations, a three dimensional image can be constructed of the plasma parameters. The colocated coherent echoes from the SuperDARN radars provide information on field aligned irregularities, and from all-sky imagers located in Resolute Bay, Canada and Qaanaaq, Greenland, information is obtained on the emission brightness at different wavelengths. A good correlation is found between the location of the coherent, incoherent and optical signals of patches. From the SuperDARN radar data it is evident that plasma irregularities seem to be present throughout the region of enhanced electron density. The patches are observed to be formed in the cusp region due to bursty flux transfer events and are then transported across the polar cap. During the time period of about 10 minutes when a patch drifted through the RISR-N field of view, the patch seemed to undergo significant deformation in all three spatial dimensions, with density fluctuations of about 10% and spatial variations leading to stretching and tilting of the patch. The findings show that plasma structuring can likely occur within polar cap patches, which support previous suggestions that a patch is highly variable as it drifts across the polar cap, with a faster spread of irregularities throughout the patch as a result. © 2012. American Geophysical Union.

    DOI: 10.1029/2012JA017961

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  245. Space-time variability of polar cap patches: Direct evidence for internal plasma structuring Reviewed

    Dahlgren H.

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 9 )   2012

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    DOI: 10.1029/2012JA017961

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  246. Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes Reviewed

    Nomura R.

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 2 )   2012

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    DOI: 10.1029/2011JA017241

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  247. Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes Reviewed

    R. Nomura, K. Shiokawa, K. Sakaguchi, Y. Otsuka, M. Connors

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 2 )   2012

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    We have investigated the polarization of Pc1 geomagnetic pulsations and related proton auroras at subauroral latitudes, using an induction magnetometer and an all-sky camera at Athabasca, Canada (54.7°N, 246.7°E, magnetic latitude (mlat) 61.7°N). Isolated proton auroras often appear in association with Pc1 pulsations, because of proton scattering by electromagnetic ion cyclotron (EMIC) waves in the magnetosphere. We used the proton aurora as a proxy for the location and size of the Pc1 ionospheric source. For 27 Pc1 events with simultaneously observed proton auroras over 4years from September 7, 2005 to September 6, 2009, we calculated the distances between the Pc1 ionospheric source and the observation site, normalized by the scale size of the source. We tried three different definitions of the scale size of Pc1 ionospheric source to calculate the normalized distances. We found that the rotation angle θ between the Pc1 polarization ellipse and the direction to the proton aurora changes from 90° to 0° as the normalized distance increases. For the definition of the scale sizes that gives most clear θ-transition from 90° to 0°, the transition occurs at the normalized distance ∼2.0-4.0, while it was ∼1.0-2.0 by the model calculation of Fujita and Tamao (1988). The averaged major axes tend to point toward the proton aurora at larger distances. The difference of the transition location may imply that the Pc1 ionospheric sources are larger than the isolated proton auroras, or that the inhomogenuity of the ionospheric conductivity by the proton precipitation affects the transition distances. Copyright 2012 by the American Geophysical Union.

    DOI: 10.1029/2011JA017241

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  248. On post-midnight field-aligned irregularities observed with a 30.8-MHz radar at a low latitude: Comparison with F-layer altitude near the geomagnetic equator Reviewed

    Nishioka M.

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 8 )   2012

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    DOI: 10.1029/2012JA017692

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  249. On post-midnight field-aligned irregularities observed with a 30.8-MHz radar at a low latitude: Comparison with F-layer altitude near the geomagnetic equator Reviewed

    M. Nishioka, Y. Otsuka, K. Shiokawa, T. Tsugawa, Null Effendy, P. Supnithi, T. Nagatsuma, K. T. Murata

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 8 )   2012

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    We investigated the relationship between post-midnight F-region field aligned irregularities (FAIs) and F-layer altitude by analyzing data of a 30.8-MHz radar installed 5at Kototabang, Indonesia (0.2S, 100.3E
    geomagnetic latitude 10.4S) and an ionosonde installed at Chumphon, Thailand (10.7N, 99.4E
    geomagnetic latitude 3.3N). Chumphon is located near the geomagnetic equator on approximately the same meridian as Kototabang. Case studies show that the altitude of the F-layer rose at Chumphon a half hour before the post-midnight FAIs appeared at Kototabang. The Doppler velocity of the E-region FAIs observed simultaneously by the 30.8-MHz radar was downward, indicating that the F-layer uplift was not caused by the electric field. We also investigated seasonal variations of the post-midnight FAI occurrence and the F-layer altitude. Both the post-midnight FAIs and the uplift of the F-layer were frequently seen around midnight between May and August. The seasonal variation of the midnight F-layer uplift around the geomagnetic equator coincided with that of the post-midnight FAI occurrence at Kototabang. These results suggest that the uplift of the F-layer would play an important role in the generation of post-midnight FAIs. We evaluated the linear growth rate of the Rayleigh-Taylor instability based on the altitude of the F-layer observed at Chumphon. The result shows that the uplift of the F-layer can enhance the growth rate because gravity-driven eastward electric current increases. Therefore, we interpret that the observed FAIs were accompanied by plasma bubble, the growth rate of which was reinforced by the uplifted F-layer. © 2012. American Geophysical Union. All Rights Reserved.

    DOI: 10.1029/2012JA017692

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  250. Magnetospheric responses to the passage of the interplanetary shock on 24 November 2008 Reviewed

    Kim K.H.

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 10 )   2012

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    DOI: 10.1029/2012JA017871

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  251. Visualization of ion cyclotron wave and particle interactions in the inner magnetosphere via THEMIS-ASI observations Reviewed

    K. Sakaguchi, Y. Miyoshi, E. Spanswick, E. Donovan, I. R. Mann, V. Jordanova, K. Shiokawa, M. Connors, J. C. Green

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 10 )   2012

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    Interaction with EMIC (electromagnetic ion cyclotron) waves is thought to be a key component contributing to the very rapid loss of both ring current and radiation belt particles into the atmosphere. Estimated loss rates are heavily dependent on the assumed spatial distribution of the EMIC wave. Statistical maps of the spatial distribution have been produced using in-situ satellite data. However, with limited satellite data it is impossible to deduce the true spatial distribution. In this study, we present ground-based observations using all-sky imager and search coil magnetometer networks, which provide the large-scale distribution and motion of the EMIC wave-particle interaction regions. We observed several spots of isolated proton auroras simultaneously with Pc1/EMIC waves at subauroral latitudes during the expansion phase of a storm-time substorm on 9 March 2008. The isolated auroras were distributed over ∼4-hours MLT preceding midnight. The POES-17 satellite confirmed enhancements of 30-keV proton precipitations over the isolated auroras. The equatorward motion of the auroras and frequency drift of the wave were consistent with the plasmasphere eroding due to a polar cap potential enhancement modeled by a numerical simulation. We also found that relativistic electron precipitation was not always associated with the isolated aurora, depending strongly on the plasma density profile near the plasmapause. This study shows that the specific distribution of ring current proton precipitation can be visualized through the ground network observations. By combining with upcoming inner-magnetosphere satellite missions, these remote-sensing observations are very important for quantitative understanding of the particle loss in the inner magnetosphere. ©2012. American Geophysical Union. All Rights Reserved.

    DOI: 10.1029/2012JA018180

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  252. Visualization of ion cyclotron wave and particle interactions in the inner magnetosphere via THEMIS-ASI observations Reviewed

    Sakaguchi K.

    Journal of Geophysical Research: Space Physics   Vol. 117 ( 10 )   2012

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    DOI: 10.1029/2012JA018180

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  253. Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging Reviewed

    K. J. W. Lynn, Y. Otsuka, K. Shiokawa

    GEOPHYSICAL RESEARCH LETTERS   Vol. 38 ( 23 )   2011.12

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    Airglow observations of ionospheric electron density depletions made at Darwin, Australia have demonstrated that the tree-like structure of bubbles developed at the magnetic equator are mapped along magnetic field lines with considerable accuracy to the base of the ionosphere at higher latitudes. Ionosonde range-time displays made at Darwin and other equatorial sites in the Australian region show characteristic approaching and receding echoes which converge on a typical spread-F event. These off-angle echoes have often been referred to in the literature as satellite traces and associated with spread F with little recognition of their true significance. All four optical depletions previously reported in the literature as being seen at Darwin are found in this paper to be accompanied by such typical off-angle/spread F events. The zonal drift velocity of the moving reflectors can be measured from the speed at which such echoes approach and recede. Since digital ionosondes in equatorial sites have existed for many years, existing ionogram data, when suitably processed into range-time displays, may allow the occurrence of such events over several sunspot cycles to be found. A question remains as to whether all or only some of such equatorial range-time events correspond to electron density depletions. Citation: Lynn, K. J. W., Y. Otsuka, and K. Shiokawa (2011), Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging, Geophys. Res. Lett., 38, L23101, doi:10.1029/2011GL049856.

    DOI: 10.1029/2011GL049856

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  254. A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) Reviewed

    Lee S., Shiokawa K., McFadden J. P., Nishimura Y.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.12

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    DOI: 10.1029/2011JA016954

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  255. High-latitude GPS TEC changes associated with a sudden magnetospheric compression Reviewed

    P. T. Jayachandran, C. Watson, I. J. Rae, J. W. MacDougall, D. W. Danskin, R. Chadwick, T. D. Kelly, P. Prikryl, K. Meziane, K. Shiokawa

    GEOPHYSICAL RESEARCH LETTERS   Vol. 38 ( 23 )   2011.12

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    Using ionospheric total electron content (TEC) measured by Global Positioning System (GPS) receivers of the Canadian High Arctic Ionospheric Network (CHAIN) we provide clear evidence for a systematic and propagating temporary TEC enhancement produced by compression of the magnetosphere due to a sudden increase in solar wind dynamic pressure. The magnetospheric compression is evident in THEMIS/GOES satellite data. Application of a GPS triangulation technique revealed that the TEC changes propagated with a speed of 3-6 km/s in the antisunward direction near noon and similar to 8 km/s in the sunward direction in the pre-noon lower latitude sector. Characteristics of these TEC changes along with riometer absorption measurements seems to indicate that the TEC change is due to electron density enhancement in the F region and is possibly due to particle precipitation associated with sudden magnetospheric compression. Citation: Jayachandran, P. T., C. Watson, I. J. Rae, J. W. MacDougall, D. W. Danskin, R. Chadwick, T. D. Kelly, P. Prikryl, K. Meziane, and K. Shiokawa (2011), Highlatitude GPS TEC changes associated with a sudden magnetospheric compression, Geophys. Res. Lett., 38, L23104, doi: 10.1029/2011GL050041.

    DOI: 10.1029/2011GL050041

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  256. A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) Reviewed

    S. Lee, K. Shiokawa, J. P. McFadden, Y. Nishimura

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.12

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    We have statistically investigated the electron density n(e,M) and temperature T(e,M) in the near-Earth plasma sheet in terms of the magnetosphere-ionosphere coupling process, as measured by the electrostatic analyzer (ESA) on board the Time History of Events and Macroscale Interactions during Substorms (THEMIS-D) satellite from November 2007 to January 2010. To find out when and where an aurora can occur, either with or without electron acceleration, the thermal current j(parallel to)(th) and the conductivity K along the magnetic field line were also estimated from observations of the magnetospheric electrons with pitch angle information inside 12 R(E). The thermal current, j(parallel to)(th)(proportional to n(e,M) T(e,M)(1/2)), represents the upper limit of the field-aligned current that can be carried by magnetospheric electrons without a field-aligned potential difference. The conductivity, K(proportional to n(e,M) T(e,M)(-1/2)), relates the upward field-aligned current, j(parallel to), to the field-aligned potential difference, V(parallel to), assuming adiabatic electron transport. The thermal current is estimated by two methods: (1) from the relation by using n(e,M) and T(e,M) and (2) from the total downward electron number flux. We find that in the dawnside inner magnetosphere, the thermal currents estimated by both methods are sufficient to carry typical region 2 upward field-aligned current. On the other hand, in the duskside outer magnetosphere, a field-aligned potential difference is necessary on the region 1 current since the estimated thermal current is smaller than the typical region 1 current. By using the relationship, j(parallel to) = KV(parallel to), where K is the conductivity estimated from Knight&apos;s relation and j. is the typical auroral current, we conclude that a field-aligned potential difference of V(parallel to) = 2-5 kV is necessary on the duskside region 1 upward field-aligned current.

    DOI: 10.1029/2011JA016954

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  257. Long-term variations in tweek reflection height in the D and lower E regions of the ionosphere Reviewed

    Hiroyo Ohya, Kazuo Shiokawa, Yoshizumi Miyoshi

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116 ( 10 )   2011.10

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    We investigated, for the first time, long-term (1976-2010) variations in reflection heights of tweek atmospherics based on very low frequency (VLF) observations at Kagoshima, Japan. The results revealed the effects of the solar cycle on the nighttime lower ionosphere at low to middle latitudes. The tweek reflection heights on geomagnetically quiet days were analyzed every month over three solar cycles by using an automated spectral fitting procedure to estimate the cutoff frequency. The average and standard deviation of the reflection height were 95.9 km and +/-3.1 km, respectively. Typical periods of time variation for the reflection height were 13.3, 3.2, 1.3, 1.0, 0.6, and 0.5 years. The variations in tweek reflection heights did not show simple anticorrelation with solar activity. The correlation coefficient between tweek reflection height and sunspot number was 0.03 throughout the three solar cycles. Hilbert-Huang transform analysis successfully indicated the presence of 0.5-1.5 year and similar to 10 year variations as intrinsic mode functions (IMF). The decomposed IMF with the similar to 10 year variation had a positive correlation with sunspot numbers and a negative correlation with galactic cosmic rays (GCRs). We hypothesize that these variations in tweek reflection heights could be caused by coupling of several ionization effects at the D and lower E regions, effects such as geocorona, GCRs, particle precipitation, and variations in neutral density in the lower thermosphere. Among these processes, the geocorona and particle precipitation could show negative correlation, while the GCRs and neutral density could show positive correlation with solar activities.

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  258. ジオスペース探査ERG計画 Reviewed

    小野 高幸, 浅村 和史, 三好 由純, 高島 健, 平原 聖文, 小原 隆博, 笠羽 康正, 熊本 篤志, 松岡 彩子, 小嶋 浩嗣, 塩川 和夫, 関 華奈子, 藤本 正樹, 長妻 努, ERGワーキンググループ

    電子情報通信学会技術研究報告. SANE, 宇宙・航行エレクトロニクス   Vol. 111 ( 239 ) page: 57 - 61   2011.10

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    ジオスペースERG探査計画の紹介.

    CiNii Article

    Other Link: http://repository.kulib.kyoto-u.ac.jp/dspace/handle/2433/193849

  259. An empirical model of the quiet daily geomagnetic field variation Reviewed

    Y. Yamazaki, K. Yumoto, M. G. Cardinal, B. J. Fraser, P. Hattori, Y. Kakinami, J. Y. Liu, K. J. W. Lynn, R. Marshall, D. McNamara, T. Nagatsuma, V. M. Nikiforov, R. E. Otadoy, M. Ruhimat, B. M. Shevtsov, K. Shiokawa, S. Abe, T. Uozumi, A. Yoshikawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.10

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    An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp &lt;= 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit north-south asymmetry; the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season; seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity.

    DOI: 10.1029/2011JA016487

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  260. Ground-based multispectral high-speed imaging of flickering aurora Reviewed

    Ryuho Kataoka, Yoshizumi Miyoshi, Takeshi Sakanoi, Ayumi Yaegashi, Yusuke Ebihara, Kazuo Shiokawa

    GEOPHYSICAL RESEARCH LETTERS   Vol. 38 ( 14 )   2011.7

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    It has been suggested that dispersive Alfven waves (DAWs) are capable of accelerating electrons via Landau resonance, and the interference of DAWs plays an essential role to create flickering auroral patterns. Here we show evidence that the leading front of a typical interference pattern is more energetic than the trailing part, based on ground-based high-speed imaging observations at wavelengths of 670.5 nm and 844.6 nm, which are sensitive to relatively hard and soft electrons, respectively. The fine spatial resolution of 9.5 deg field-of-view at magnetic zenith and the 100 Hz sampling rate of electron multiplying charge-coupled device (EMCCD) enabled us to resolve the spatiotemporal variation of the flickering aurora. It is found that there is only 10 ms time delay with 0.5 km spatial shift on average in the obtained flickering patterns at two wavelengths. The time delay and spatial shift can be comprehensively explained by the traveling inhomogeneous interference pattern of DAWs, probably associated with the Landau damping and/or time-of-flight effect, which is only detectable using the highest resolved temporal and spatial observations of flickering aurora. Citation: Kataoka, R., Y. Miyoshi, T. Sakanoi, A. Yaegashi, Y. Ebihara, and K. Shiokawa (2011), Ground-based multispectral high-speed imaging of flickering aurora, Geophys. Res. Lett., 38, L14106, doi:10.1029/2011GL048317.

    DOI: 10.1029/2011GL048317

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  261. Decay of polar cap patch Reviewed

    K. Hosokawa, J. I. Moen, K. Shiokawa, Y. Otsuka

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 5 )   2011.5

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    We report an event in which a polar cap patch was detected with an all-sky imager (ASI) at Resolute Bay, Canada (74.73° N, 265.07° E
    AACGM latitude 82.9°), on the nightside. The patch stopped its antisunward motion associated with a northward turning of interplanetary magnetic field and stayed within the field of view of the ASI for more than 1 h. When the patch stagnated, its luminosity decreased gradually, which allows us to investigate how the patch plasma decayed in a quantitative manner. The decay of the patch can be quantitatively explained by the loss through recombinations of O+ with ambient N2 and O2 molecules, if we assume the altitude of the optical patch to be around 295 km. The derived altitude of the patch around 295 km is much higher than the nominal value at 235 km obtained from the MSIS-E90 and IRI-2007 models, indicating that climatological models such as IRI are not suitable for describing the actual density profile of patches. This is probably because the loss process was much faster in the lower-altitude part of the patch
    thus, the peak altitude of the patch increased as it traveled across the polar cap because of rapid recombination at the bottomside of the F region. This suggests that we should employ higher emission altitude when we investigate optical patches transported deep into the nightside polar cap. Such information is important when we compare the optical data with other instruments such as coherent radars and GPS scintillation measurements by mapping the all-sky image on the geographic coordinate system with an assumption of the patch emission altitude. Copyright 2011 by the American Geophysical Union.

    DOI: 10.1029/2010JA016297

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  262. Turbulent microstructures and formation of folds in auroral breakup arc Reviewed

    R. Kataoka, Y. Miyoshi, T. Sakanoi, A. Yaegashi, K. Shiokawa, Y. Ebihara

    Journal of Geophysical Research A: Space Physics   Vol. 116 ( 4 )   2011.4

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    We conducted a ground-based optical measurement pointing at local magnetic zenith with a narrow field of view of 9.3 degrees by 9.3 degrees, using a high-speed electron multiplier charge-coupled device camera at Poker Flat Research Range. We show evidence that auroral folds were periodically formed in a breakup arc and the luminosity is exponentially increased for about 10 s before an auroral breakup onset. The evolution of turbulent microstructures and the formation of folds may be interpreted by the nonlinear evolution of inertial Alfven wave (IAW) turbulence in the thin current sheet. On the basis of these optical observations, we discuss a possible role of the ionosphere for modulating the triggering process of the onset via the self-organization of the IAW turbulence associated with Kelvin-Helmholtz and tearing instabilities of the thin current sheet.

    DOI: 10.1029/2010JA016334

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  263. GEONETにおけるプラズマバブルに伴う全電子数変化率とロック損失との相関 Reviewed

    菊地 隼人, 中田 裕之, 津川 卓也, 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 = / Society of Atmospheric Electricity of Japan   Vol. 5 ( 1 ) page: 82-83   2011.4

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  264. First satellite-imaging observation of medium-scale traveling ionospheric disturbances by FORMOSAT-2/ISUAL Reviewed

    Toru Adachi, Yuichi Otsuka, Masashi Yamaoka, Mamoru Yamamoto, Kazuo Shiokawa, Alfred B. Chen, Rue-Ron Hsu

    GEOPHYSICAL RESEARCH LETTERS   Vol. 38 ( 4 )   2011.2

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    On the night of May 16, 2007, a satellite limb imager of FORMOSAT-2/ISUAL observed wave-like structures of the 630-nm airglow simultaneously with an all-sky imager deployed at Darwin in Australia. The height of the airglow layer was estimated as 220 km, and the structures were aligned in the northeast-southwest orientation with a wavelength of similar to 300 km and propagated toward the northwest with a phase velocity of similar to 100 m s(-1), showing typical characteristics of the nighttime medium-scale traveling ionospheric disturbances (MSTIDs). We conclude that ISUAL for the first time succeeded in observing the airglow layer altitude and airglow structures modulated by MSTID from space. Such a satellite limb airglow imaging could be a new tool to characterize ionospheric irregularities on a global level. Citation: Adachi, T., Y. Otsuka, M. Yamaoka, M. Yamamoto, K. Shiokawa, A. B. Chen, and R.-R. Hsu (2011), First satellite-imaging observation of medium-scale traveling ionospheric disturbances by FORMOSAT-2/ISUAL, Geophys. Res. Lett., 38, L04101, doi:10.1029/2010GL046268.

    DOI: 10.1029/2010GL046268

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  265. ULF impulsive magnetic response at mid-latitudes to lightning activity Reviewed

    Schekotov A., Pilipenko V., Shiokawa K., FEDOROV E.

    Earth, planets and space   Vol. 63 ( 2 ) page: 119-128   2011.2

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  266. Periodic black auroral patches at the dawnside dipolarization front during a substorm Reviewed

    K. Sakaguchi, K. Shiokawa, E. Donovan, A. Nakajima, Y. Hiraki, T. Trondsen, F. Plaschke

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 116   2011.1

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    Periodic black auroral patches were observed in the Canadian postmidnight sector by ground-based all-sky cameras during an auroral substorm. The aurora consisted of several black patches of similar to 50 km (similar to 1 degrees in longitude) scales that appeared along the equatorward edges of the proton auroras over a 3 h local time segment from Gillam to Sanikiluaq ground stations 15 min after the auroral intensification occurred in Alaska. To the best of our knowledge, this type of black auroras has never been reported before, although the surrounding luminous auroras evolve into the well-known torch structures later. In situ observations by the THEMIS satellites, three of which were close to being magnetically conjugate in the plasma sheet, as well as ground-based proton auroral observations, show that a dipolarization front and associated dawnward ion flows propagated eastward at poleward of the black patches coinciding with their appearance. The flow motions of auroras observed poleward of the black patches are possibly generated by decelerations of dawnward ion flow because of the consistency of both durations and positions. We speculate, based on manifestations of high-pressure regions in dipolarized flux tubes, the pressure-driven interchange instability formed a beading shape (periodic black patches) of field-aligned currents. The black auroral patches developed into torch structures after the flow disappearance, indicating the dawnward flows might stabilize and limit the instability within a narrow L shell where the pressure gradient is directed Earthward and flows cannot enter. We conclude that the periodic black patches arise as a consequence of a relaxation process of enhanced plasma pressure near the inner boundary of the plasma sheet during a substorm.

    DOI: 10.1029/2010JA015957

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  267. ULF impulsive magnetic response at mid-latitudes to lightning activity Reviewed

    A. Schekotov, V. Pilipenko, K. Shiokawa, E. Fedorov

    EARTH PLANETS AND SPACE   Vol. 63 ( 2 ) page: 119 - 128   2011

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    Induction magnetometer data from the mid-latitude station Moshiri (geomagnetic latitude 35.6 degrees.) has been examined in search of a transient ULF response to the regional lightning activity. For many events, besides the main impulse produced by the lightning discharge, a secondary impulse delayed about 1 sec was observed. These secondary echo-impulses are probably caused by the partial reflection of wave energy of the initial lightning pulse from the upper boundary of the ionospheric Alfven resonator in the topside ionosphere. The modeling with artificial signals has shown that a multi-band spectral resonant structure (SRS) can be formed owing to the occurrence of paired pulses in analyzed time series. The statistical superposed epoch method indeed has revealed a dominance of two-pulse structure in the magnetic field background during the periods of the SRS occurrence.

    DOI: 10.5047/eps.2010.12.009

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  268. A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) Reviewed

    S. Lee, K. Shiokawa, J. P. McFadden, Y. Nishimura

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 12 )   2011

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    We have statistically investigated the electron density ne,M and temperature Te,M in the near-Earth plasma sheet in terms of the magnetosphere-ionosphere coupling process, as measured by the electrostatic analyzer (ESA) on board the Time History of Events and Macroscale Interactions during Substorms (THEMIS-D) satellite from November 2007 to January 2010. To find out when and where an aurora can occur, either with or without electron acceleration, the thermal current j∥th and the conductivity K along the magnetic field line were also estimated from observations of the magnetospheric electrons with pitch angle information inside 12 RE. The thermal current, j∥th(∝ ne,M Te,M1/2), represents the upper limit of the field-aligned current that can be carried by magnetospheric electrons without a field-aligned potential difference. The conductivity, K(∝ n e,M Te,M-1/2), relates the upward field-aligned current, j∥, to the field-aligned potential difference, V ∥, assuming adiabatic electron transport. The thermal current is estimated by two methods: (1) from the relation by using ne,M and Te,M and (2) from the total downward electron number flux. We find that in the dawnside inner magnetosphere, the thermal currents estimated by both methods are sufficient to carry typical region 2 upward field-aligned current. On the other hand, in the duskside outer magnetosphere, a field-aligned potential difference is necessary on the region 1 current since the estimated thermal current is smaller than the typical region 1 current. By using the relationship, j∥ = KV∥, where K is the conductivity estimated from Knight's relation and j∥ is the typical auroral current, we conclude that a field-aligned potential difference of V∥ = 2-5 kV is necessary on the duskside region 1 upward field-aligned current. © 2011 by the American Geophysical Union.

    DOI: 10.1029/2011JA016954

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  269. Frequency-dependent polarization characteristics of Pc1 geomagnetic pulsations observed by multipoint ground stations at low latitudes Reviewed

    R. Nomura, K. Shiokawa, V. Pilipenko, B. Shevtsov

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 1 )   2011

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    We have investigated Pc1 geomagnetic pulsations observed by induction magnetometers at three low-latitude stations (Paratunka (PTK), Moshiri (MSR), and Sata (STA), L=1.2-2.1). A detailed polarization analysis shows that polarization parameters (angle of polarization ellipse orientation, ψ, and polarization sense, ε) of individual Pc1 bands depend on frequency at all three stations. The dependence of ψ on frequency was seen in ∼70% of the 93 Pc1 events observed at MSR (L=1.5) from 14 July 2007 to 13 July 2009. The maxima of seasonal and diurnal variations of the occurrence rate were in winter and during the nighttime, as reported previously, indicating that the transmission of observed Pc1 pulsations to lower latitudes is controlled by the density of the F layer plasma. These facts suggest that spatially distributed Pc1 waves with varying frequencies depending on longitude or latitude at high latitudes propagated in the ionospheric duct to cause the frequency dependence of polarization parameters at low latitudes. We also suggest that the Pc1 pearl structure with a repetition period of ∼5-30 s observed at low latitudes is a beat of high-latitude waves with slightly different frequencies. Copyright 2011 by the American Geophysical Union.

    DOI: 10.1029/2010JA015684

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  270. Atmospheric wave induced O-2 and OH airglow intensity variations: effect of vertical wavelength and damping Reviewed

    H. Takahashi, A. Onohara, K. Shiokawa, F. Vargas, D. Gobbi

    ANNALES GEOPHYSICAE   Vol. 29 ( 4 ) page: 631 - 637   2011

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    DOI: 10.5194/angeo-29-631-2011

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  271. An empirical model of the quiet daily geomagnetic field variation Reviewed

    Yamazaki Y.

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 10 )   2011

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    DOI: 10.1029/2011JA016487

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  272. An empirical model of the quiet daily geomagnetic field variation Reviewed

    Y. Yamazaki, K. Yumoto, M. G. Cardinal, B. J. Fraser, P. Hattori, Y. Kakinami, J. Y. Liu, K. J.W. Lynn, R. Marshall, D. McNamara, T. Nagatsuma, V. M. Nikiforov, R. E. Otadoy, M. Ruhimat, B. M. Shevtsov, K. Shiokawa, S. Abe, T. Uozumi, A. Yoshikawa

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 10 )   2011

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    An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp ≤ 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit north-south asymmetry
    the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season
    seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity. Copyright 2011 by the American Geophysical Union.

    DOI: 10.1029/2011JA016487

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  273. A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) Reviewed

    Lee S.

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 12 )   2011

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    Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research: Space Physics  

    DOI: 10.1029/2011JA016954

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  274. Motion of polar cap arcs Reviewed

    Hosokawa, K, J. I. Moen, K. Shiokawa, Y. Otsuka

    Journal of Geophysical Research   Vol. 116   page: doi:10.1029/2010JA015906   2011

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  275. Statistical Study of Medium-Scale Traveling Ionospheric Disturbances Observed with a GPS Receiver Network in Japan Reviewed

    Otsuka, Y, Kotake, N, Shiokawa, K, Ogawa, T, Tsugawa, T, Saito, A

    AERONOMY OF THE EARTH'S ATMOSPHERE AND IONOSPHERE   Vol. 2   page: 291 - 299   2011

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    DOI: 10.1007/978-94-007-0326-1_21

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  276. Periodic black auroral patches at the dawnside dipolarization front during a substorm Reviewed

    Sakaguchi K.

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 1 )   2011

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    DOI: 10.1029/2010JA015957

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  277. Periodic black auroral patches at the dawnside dipolarization front during a substorm Reviewed

    K. Sakaguchi, K. Shiokawa, E. Donovan, A. Nakajima, Y. Hiraki, T. Trondsen, F. Plaschke

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 1 )   2011

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

    Periodic black auroral patches were observed in the Canadian postmidnight sector by ground-based all-sky cameras during an auroral substorm. The aurora consisted of several black patches of ∼50 km (∼1° in longitude) scales that appeared along the equatorward edges of the proton auroras over a 3 h local time segment from Gillam to Sanikiluaq ground stations 15 min after the auroral intensification occurred in Alaska. To the best of our knowledge, this type of black auroras has never been reported before, although the surrounding luminous auroras evolve into the well-known torch structures later. In situ observations by the THEMIS satellites, three of which were close to being magnetically conjugate in the plasma sheet, as well as ground-based proton auroral observations, show that a dipolarization front and associated dawnward ion flows propagated eastward at poleward of the black patches coinciding with their appearance. The flow motions of auroras observed poleward of the black patches are possibly generated by decelerations of dawnward ion flow because of the consistency of both durations and positions. We speculate, based on manifestations of high-pressure regions in dipolarized flux tubes, the pressure-driven interchange instability formed a beading shape (periodic black patches) of field-aligned currents. The black auroral patches developed into torch structures after the flow disappearance, indicating the dawnward flows might stabilize and limit the instability within a narrow L shell where the pressure gradient is directed Earthward and flows cannot enter. We conclude that the periodic black patches arise as a consequence of a relaxation process of enhanced plasma pressure near the inner boundary of the plasma sheet during a substorm. Copyright 2011 by the American Geophysical Union.

    DOI: 10.1029/2010JA015957

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  278. Motion of polar cap arcs Reviewed

    Hosokawa K., Moen J.I., Shiokawa K., Otsuka Y.

    Journal of Geophysical Research: Space Physics   Vol. 116 ( 1 )   2011

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research: Space Physics  

    A statistics of motion of polar cap arcs is conducted by using 5 years of optical data from an all-sky imager at Resolute Bay, Canada (74.73°N, 265.07°E). We identified 743 arcs by using an automated arc detection algorithm and statistically examined their moving velocities as estimated by the method of Hosokawa et al. (2006). The number of the arcs studied is about 5 times larger than that in the previous statistics of polar cap arcs by Valladares et al. (1994); thus, we could expect to obtain more statistically significant results. Polar cap arcs are found to fall into two distinct categories: the By-dependent and By-independent arcs. The motion of the former arcs follows the rule reported by Valladares et al. (1994), who showed that stable polar cap arcs move in the direction of the interplanetary magnetic field (IMF) By. About two thirds of the arcs during northward IMF conditions belong to this category. The latter arcs always move poleward irrespective of the sign of the IMF By, which possibly correspond to the poleward moving arcs in the morning side reported by Shiokawa et al. (1997). At least one third of the arcs belong to this category. The By-dependent arcs tend to move faster when the magnitude of the IMF By is larger, suggesting that the transport of open flux by lobe reconnection from one polar cap compartment to the other controls their motion. In contrast, the speed of the By-independent arcs does not correlate with the magnitude of the By. The motions of both the B y-dependent and By-independent arcs are most probably caused by the magnetospheric convection. Convection in the region of B y-dependent arcs is affected by the IMF By, which indicates that their sources may be on open field lines or in the closed magnetosphere adjacent to the open-closed boundary, whereas B y-independent arcs seem to be well on closed field lines. Hence, the magnetospheric source of the two types of arc may be different. This implies that the mechanisms causing the motion and generation of arcs could be different between the two types of polar cap arc. Copyright 2011 by the American Geophysical Union.

    DOI: 10.1029/2010JA015906

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  279. Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm Reviewed

    Hosokawa K., Tsugawa T., Shiokawa K., Otsuka Y., Nishitani N., Ogawa T., Hairston M. R.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.12

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    DOI: 10.1029/2010JA015848

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  280. Simultaneous airglow, lidar, and radar measurements of mesospheric gravity waves over Japan Reviewed

    Suzuki S., Nakamura T., Ejiri M. K., Tsutsumi M., Shiokawa K., Kawahara T. D.

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES   Vol. 115   2010.12

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    DOI: 10.1029/2010JD014674

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  281. Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm Reviewed

    K. Hosokawa, T. Tsugawa, K. Shiokawa, Y. Otsuka, N. Nishitani, T. Ogawa, M. R. Hairston

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.12

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    During a magnetic storm on 14-16 December 2006, a polar cap tongue of ionization (TOI) was detected by an all-sky imager (ASI) at Resolute Bay, Canada (74.73 degrees N, 265.07 degrees E). We investigate the temporal evolution and spatial structure of the TOI in detail by combining the optical data with other observations (e. g., solar wind, GPS total electron content, SuperDARN, and DMSP and NOAA POES satellites). The TOI was observed as a bright and elongated 630 nm airglow plume for 4 h during the main phase of the storm. This interval corresponded to a period of prolonged stable large-amplitude southward IMF during a coronal mass ejection (CME). One to one and a half hours before the appearance of TOI, the polar cap boundary expanded rapidly far equatorward, and a positive ionospheric storm occurred. This implies that both the "expansion of the high-latitude plasma convection" and "build up of the source plasma in the midlatitudes" are necessary conditions for the formation of a TOI. Because both of them were triggered by a major southward turning of the IMF, the prolonged large-amplitude southward IMF orientation in the trailing part of the CME was primarily responsible for the generation of TOI. After its appearance, the TOI exhibited dynamic motion in the dawn to dusk direction. Simultaneous SuperDARN data suggest that a longitudinal progression of subauroral polarization stream controlled this dynamic motion. The optical TOI was found to be a continuous stream elongated in the noon-midnight direction although it contained some mesoscale patterns. Absence of large-scale temporal changes in the cusp plasma flow during the stable IMF period allowed the TOI to remain continuous without being broken into polar cap patches. The mesoscale structures within the TOI were probably produced by small-scale velocity fluctuations in the cusp plasma flow. The TOI as visualized with the all-sky airglow imager was found to be much more dynamic and much more complicated than we ever thought. The current study indicates that such a behavior of the TOI was presumably caused by a combination of temporal variations in the global-scale plasma circulation system, expansion and contraction of the polar cap area, and plasma density changes in the dayside low to midlatitudes.

    DOI: 10.1029/2010JA015848

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  282. Simultaneous airglow, lidar, and radar measurements of mesospheric gravity waves over Japan Reviewed

    S. Suzuki, T. Nakamura, M. K. Ejiri, M. Tsutsumi, K. Shiokawa, T. D. Kawahara

    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES   Vol. 115   2010.12

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    To investigate gravity wave dynamics in the mesosphere and lower thermosphere (MLT) region, we conducted coordinated observations of mesospheric gravity waves over Japan during the Aeronomy and Dynamics Observation campaign. Two all-sky airglow imagers were used in this campaign to derive a two-dimensional structure of the gravity waves; these imagers were installed at the middle and upper atmosphere (MU) observatory in Shigaraki (34.9 degrees N, 136.1 degrees E) and at the Dynic Astropark Observatory in Taga (35.2 degrees N, 136.3 degrees E). Simultaneous measurements of the horizontal winds and the temperature in the MLT region were provided by the meteor-mode observations of the MU radar at Shigaraki and by a sodium temperature lidar at Uji (34.9 degrees N, 135.8 degrees E), respectively. On 2 October 2008, gravity waves having a horizontal wavelength of similar to 170 km, wave period of similar to 1 h, and propagating northeastward at similar to 50 m s(-1) were observed in the airglow keograms. Similar wave structures were observed in the time series of the meteor wind and lidar temperature data; the polarity of these waves varied consistently with the airglow intensity variations according to the linear theory of gravity waves. The phase speeds and momentum fluxes of the gravity waves, estimated from the wind and temperature observations, were also in good agreement with those obtained from the airglow measurements. These results demonstrate, both qualitatively and quantitatively, that an identical gravity wave structure was detected in all the airglow intensities, radar winds, and lidar temperature.

    DOI: 10.1029/2010JD014674

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  283. プラズマバブルに伴う全電子数変化率・ロック損失分布 : ロック損失発生の有無と全電子数変化率の相関 Reviewed

    菊地 隼人, 中田 裕之, 津川 卓也, 大塚 雄一, 西岡 未知, 鷹野 敏明, 島倉 信, 塩川 和夫, 小川 忠彦

    大気電気学会誌 = / Society of Atmospheric Electricity of Japan   Vol. 4 ( 2 ) page: 80-81   2010.10

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  284. Simultaneous FAST and Double Star TC1 observations of broadband electrons during a storm time substorm Reviewed

    A. Nakajima, K. Shiokawa, K. Seki, R. Nakamura, K. Keika, W. Baumjohann, T. Takada, J. P. McFadden, C. W. Carlson, A. N. Fazakerley, H. Reme, I. Dandouras, R. J. Strangeway, O. Le Contel, N. Cornilleau-Wehrlin, K. H. Yearby

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.7

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    Broadband electrons (BBEs) exhibit remarkable electron flux enhancements over a broad energy range (0.03-30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. Here, we report a BBE event observed by the Fast Auroral Snapshot (FAST) satellite at 1355-1359 UT, similar to 61 degrees-66 degrees invariant latitudes, similar to 0600 magnetic local time (MLT), and similar to 3800 km altitude during a storm on 25 July 2004. The Double Star (DS) TC1 satellite was located near the magnetic equator at L = 5.7, close to the same local time as FAST. We investigate the acceleration process of BBEs from the inner magnetosphere to near the ionosphere by comparing electron data obtained by FAST and DS TC1. We also investigate both plasma and field variations in the inner magnetosphere associated with substorm onset using DS TC1 data to examine the relationship between the BBEs and the storm time substorm. Ground geomagnetic field data show a positive H-bay at similar to 1349 UT at similar to 0600 MLT, indicating that a storm time substorm started just before the appearance of the BBEs. At similar to 1350 UT, a tailward ion flow was observed by DS TC1. Then, DS TC1 observed a local dipolarization and a drastic ion density enhancement at similar to 1351 UT, indicating that particle heating associated with the substorm was occurring in the inner magnetosphere. From similar to 1352 UT, electron fluxes were isotropically enhanced at energies above similar to 0.5 keV as observed by DS TC1. On the other hand, the pitch angle distribution of BBEs at the FAST altitude showed field-aligned lower-energy electrons below similar to 0.5 keV and isotropic higher-energy electrons above similar to 0.5 keV. From these data, it was inferred that the BBEs might consist of two energy components due to the acceleration or heating of electrons at different altitudes in association with the storm time substorm.

    DOI: 10.1029/2009JA014907

    Web of Science

  285. The STEL induction magnetometer network for observation of high-frequency geomagnetic pulsations Reviewed

    Shiokawa K., Nomura R., Sakaguchi K., OTSUKA Y., HAMAGUCHI Y., SATOH M., KATOH Y., YAMAMOTO Y., SHEVTSOV B. M., SMIRNOV S., PODDELSKY I., CONNORS M.

    Earth, planets and space   Vol. 62 ( 6 ) page: 517-524   2010.6

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    CiNii Article

  286. プラズマバブルに伴うGPSロック損失・全電子数変化率分布のマルチイベント解析 Reviewed

    菊地 隼人, 中田 裕之, 津川 卓也, 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 = / Society of Atmospheric Electricity of Japan   Vol. 4 ( 1 ) page: 58-59   2010.4

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    CiNii Article

  287. Rayleigh-Taylor type instability in auroral patches Reviewed

    K. Shiokawa, A. Nakajima, A. Ieda, K. Sakaguchi, R. Nomura, T. Aslaksen, M. Greffen, E. Donovan

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.2

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

    Based on observations by a high-resolution narrow field-of-view CCD camera, we found small-scale (5-25 km) finger-like structures at the western boundary of auroral patches in images obtained at Gillam (geomagnetic latitude: 65.5 degrees N), Canada, in January 2008. Since shear motion was not observed along the boundary of the patches, we suggest that these structures are formed by macroscopic Rayleigh-Taylor type plasma instability arising in the magnetospheric equatorial plane from the force balancing of the (eastward) magnetic tension force and the (westward) pressure gradient force.

    DOI: 10.1029/2009JA014273

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  288. A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes Reviewed

    Balan N., Shiokawa K., Otsuka Y., Kikuchi T., Lekshmi D. Vijaya, Kawamura S., Yamamoto M., Bailey G. J.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.2

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    DOI: 10.1029/2009JA014515

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  289. A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes Reviewed

    Balan N.

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 2 )   2010.2

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    DOI: 10.1029/2009JA014515

    Scopus

  290. A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes Reviewed

    N. Balan, K. Shiokawa, Y. Otsuka, T. Kikuchi, D. Vijaya Lekshmi, S. Kawamura, M. Yamamoto, G. J. Bailey

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.2

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

    A physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi-instrument observations, theoretical modeling, and basic principles. According to the mechanism, an equatorward neutral wind is required to produce positive ionospheric storms. The mechanical effects of the wind (1) reduce (or stop) the downward diffusion of plasma along the geomagnetic field lines, (2) raise the ionosphere to high altitudes of reduced chemical loss, and hence (3) accumulate the plasma at altitudes near and above the ionospheric peak centered at around +/- 30 degrees magnetic latitudes. Daytime eastward prompt penetration electric field (PPEF), if it occurs, also shifts the equatorial ionization anomaly crests to higher than normal latitudes, up to approximately +/- 30 degrees latitudes. The positive ionospheric storms are most likely in the longitudes where the onset of the geomagnetic storms falls in the ionization production dominated morning-noon local time sector when the plasma accumulation due to the mechanical effects of the wind largely exceeds the plasma loss due to the chemical effect of the wind. The mechanism agrees with the multi-instrument observations made during the supergeomagnetic storm of 7-8 November 2004, with 18 h long initial phase (IP) and 10 h long main phase (MP). The observations, which are mainly in the Japanese-Australian longitudes where the MP onset was in the morning (0600 LT, 2100 UT), show (1) strong positive ionospheric storms (in Ne, Nmax, hmax, Global Positioning System-total electron content (GPS-TEC), and 630 nm airglow intensity) in both Northern and Southern hemispheres started at the morning (0600 LT) MP onset and lasted for a day, (2) repeated occurrence of strong eastward PPEF events penetrated after the MP onset and superposed with westward electric field started before the MP onset, and (3) storm time equatorward neutral winds (inferred from 1 and 2). Repeated occurrence of an unusually strong F-3 layer with large density depletions around the equator was also observed during the morning-noon MP.

    DOI: 10.1029/2009JA014515

    Web of Science

  291. Reorganization of polar cap patches through shears in the background plasma convection Reviewed

    Hosokawa K., St-Maurice J. -P., Sofko G. J., Shiokawa K., Otsuka Y., Ogawa T.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.1

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    DOI: 10.1029/2009JA014599

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  292. Reorganization of polar cap patches through shears in the background plasma convection Reviewed

    K. Hosokawa, J. -P. St-Maurice, G. J. Sofko, K. Shiokawa, Y. Otsuka, T. Ogawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 115   2010.1

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

    On the night of December 20, 2006, 630 nm airglow images obtained by an all-sky camera at Resolute Bay, Canada (74.73 degrees N, 265.07 degrees E; altitude adjusted corrected geomagnetic (AACGM) latitude 82.9 degrees) showed the passage of successive polar cap patches. Shortly after convection came to a temporary halt, one of the patches was reorganized into two substructures in approximately 8 min. The two-dimensional background ionospheric convection pattern measured using the newly deployed PolarDARN radar at Rankin Inlet (62.82 degrees N, 93.11 degrees W; AACGM latitude 72.96 degrees) showed that a velocity shear of approximately 120 m s(-1)/340 km suddenly appeared in the vicinity of the patch at the time of reorganization. A qualitative analysis of the relationship between the magnitude of the velocity shear and the distance between the divided patches indicates that the shear in the background plasma convection velocity significantly contributed to the reorganization of the patch. This shear structure appeared soon after a southward turning of the interplanetary magnetic field (IMF) and was probably associated with the reconfiguration of the convection pattern from a pre-existing northward-oriented IMF pattern to a southward-oriented one. The present observations indicate that the reconfiguration/deformation of patches because of a shear in the background convection field, especially reorganization of patches into smaller substructures, may play an important role in the rapid structuring of patches.

    DOI: 10.1029/2009JA014599

    Web of Science

  293. Reorganization of polar cap patches through shears in the background plasma convection Reviewed

    Hosokawa K.

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 1 )   2010.1

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    DOI: 10.1029/2009JA014599

    Scopus

  294. Rayleigh-Taylor type instability in auroral patches Reviewed

    Shiokawa, K., A. Nakajima, A. Ieda, K. Sakaguchi, R. Nomura, T. Aslaksen, M. Greffen,and E. Donovan

    J. Geophys. Res   Vol. 115 ( A02211 ) page: doi:10.1029/2009JA014273   2010

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  295. The STEL induction magnetometer network for observation of high-frequency geomagnetic pulsations Reviewed

    Shiokawa, K., R. Nomura, K. Sakaguchi, Y. Otsuka, Y. Hamaguchi, M. Satoh, Y. Katoh, Y. Yamamoto, B. M. Shevtsov, S. Smirnov, I. Poddelsky, and M. Connors

    Earth Planets and Space   Vol. 62   page: 517-524   2010

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  296. The STEL induction magnetometer network for observation of high-frequency geomagnetic pulsations Reviewed

    K. Shiokawa, R. Nomura, K. Sakaguchi, Y. Otsuka, Y. Hamaguchi, M. Satoh, Y. Katoh, Y. Yamamoto, B. M. Shevtsov, S. Smirnov, I. Poddelsky, M. Connors

    EARTH PLANETS AND SPACE   Vol. 62 ( 6 ) page: 517 - 524   2010

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER HEIDELBERG  

    The Solar-Terrestrial Environment Laboratory (STEL) induction magnetometer network has been developed to investigate the propagation characteristics of high-frequency geomagnetic pulsations in the Pc1 frequency range (0.2-5 Hz). Five induction magnetometers were installed in the period 2005-2008 at Athabasca in Canada, Magadan and Paratunka in Far East Russia, and Moshiri and Sata in Japan. The sensitivity of these magnetometers is between 0.3 and 13 V/nT at turnover frequencies of 1.7-5.5 Hz. GPS time pulses are used for accurate triggering of the 64-Hz data sampling. We show examples of PiB/Pc1 magnetic pulsations observed at these five stations, as well as the harmonic structure of ionospheric Alfven resonators observed at Moshiri. We found that the Pc1 packets are slightly modulated as they propagate from high to low latitudes in the ionospheric duct. These network observations are expected to contribute to our understanding of Pc1-range magnetic pulsations and their interaction with relativistic electrons by combining the obtained results with future satellite missions that observe radiation belt particles.

    DOI: 10.5047/eps.2010.05.003

    Web of Science

    Scopus

  297. Erratum: Geospace Exploration Mission: ERG Project Reviewed

    MIYOSHI Yoshizumi, MATSUOKA Ayako, NAGATSUMA Tsutomu, Working Group ERG, SEKI Kanako, SHIOKAWA Kazuo, ONO Takayuki, KASABA Yasumasa, KUMAMOTO Atsushi, HIRAHARA Masafumi, TAKASHIMA Takeshi, ASAMURA Kazushi

    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN   Vol. 8 ( 27 )   2010

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    DOI: 10.2322/tastj.8.Tm_13

    CiNii Article

  298. Geospace Exploration Mission: ERG Project Reviewed

    MIYOSHI Yoshizumi, MATSUOKA Ayako, NAGATSUMA Tsutomu, Working Group ERG, SEKI Kanako, SHIOKAWA Kazuo, ONO Takayuki, KASABA Yasumasa, KUMAMOTO Atsushi, HIRAHARA Masafumi, TAKASHIMA Takeshi, ASAMURA Kazushi

    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN   Vol. 8 ( 27 ) page: Tm_1-Tm_6   2010

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    DOI: 10.2322/tastj.8.Tm_1

    CiNii Article

  299. A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes Reviewed

    N. Balan, K. Shiokawa, Y. Otsuka, T. Kikuchi, D. Vijaya Lekshmi, S. Kawamura, M. Yamamoto, G. J. Bailey

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 2 )   2010

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

    [1] A physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi-instrument observations, theoretical modeling, and basic principles. According to the mechanism, an equatorward neutral wind is required to produce positive ionospheric storms. The mechanical effects of the wind (1) reduce (or stop) the downward diffusion of plasma along the geomagnetic field lines, (2) raise the ionosphere to high altitudes of reduced chemical loss, and hence (3) accumulate the plasma at altitudes near and above the ionospheric peak centered at around ±30° magnetic latitudes. Daytime eastward prompt penetration electric field (PPEF), if it occurs, also shifts the equatorial ionization anomaly crests to higher than normal latitudes, up to approximately ±30° latitudes. The positive ionospheric storms are most likely in the longitudes where the onset of the geomagnetic storms falls in the ionization production dominated morning-noon local time sector when the plasma accumulation due to the mechanical effects of the wind largely exceeds the plasma loss due to the chemical effect of the wind. The mechanism agrees with the multi-instrument observations made during the supergeomagnetic storm of 7-8 November 2004, with 18 h long initial phase (IP) and 10 h long main phase (MP). The observations, which are mainly in the Japanese-Australian longitudes where the MP onset was in the morning (0600 LT, 2100 UT), show (1) strong positive ionospheric storms (in Ne, Nmax, hmax, Global Positioning System-total electron content (GPS-TEC), and 630 nm airglow intensity) in both Northern and Southern hemispheres started at the morning (0600 LT) MP onset and lasted for a day, (2) repeated occurrence of strong eastward PPEF events penetrated after the MP onset and superposed with westward electric field started before the MP onset, and (3) storm time equatorward neutral winds (inferred from 1 and 2). Repeated occurrence of an unusually strong F3 layer with large density depletions around the equator was also observed during the morning-noon MP. Copyright 2010 by the American Geophysical Union.

    DOI: 10.1029/2009JA014515

    Scopus

  300. Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm Reviewed

    Hosokawa K.

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 12 )   2010

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    DOI: 10.1029/2010JA015848

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  301. Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm Reviewed

    K. Hosokawa, T. Tsugawa, K. Shiokawa, Y. Otsuka, N. Nishitani, T. Ogawa, M. R. Hairston

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 12 )   2010

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    During a magnetic storm on 14-16 December 2006, a polar cap tongue of ionization (TOI) was detected by an all-sky imager (ASI) at Resolute Bay, Canada (74.73°N, 265.07°E). We investigate the temporal evolution and spatial structure of the TOI in detail by combining the optical data with other observations (e.g., solar wind, GPS total electron content, SuperDARN, and DMSP and NOAA POES satellites). The TOI was observed as a bright and elongated 630 nm airglow plume for 4 h during the main phase of the storm. This interval corresponded to a period of prolonged stable large-amplitude southward IMF during a coronal mass ejection (CME). One to one and a half hours before the appearance of TOI, the polar cap boundary expanded rapidly far equatorward, and a positive ionospheric storm occurred. This implies that both the "expansion of the high-latitude plasma convection" and "build up of the source plasma in the midlatitudes" are necessary conditions for the formation of a TOI. Because both of them were triggered by a major southward turning of the IMF, the prolonged large-amplitude southward IMF orientation in the trailing part of the CME was primarily responsible for the generation of TOI. After its appearance, the TOI exhibited dynamic motion in the dawn to dusk direction. Simultaneous SuperDARN data suggest that a longitudinal progression of subauroral polarization stream controlled this dynamic motion. The optical TOI was found to be a continuous stream elongated in the noon-midnight direction although it contained some mesoscale patterns. Absence of large-scale temporal changes in the cusp plasma flow during the stable IMF period allowed the TOI to remain continuous without being broken into polar cap patches. The mesoscale structures within the TOI were probably produced by small-scale velocity fluctuations in the cusp plasma flow. The TOI as visualized with the all-sky airglow imager was found to be much more dynamic and much more complicated than we ever thought. The current study indicates that such a behavior of the TOI was presumably caused by a combination of temporal variations in the global-scale plasma circulation system, expansion and contraction of the polar cap area, and plasma density changes in the dayside low to midlatitudes. Copyright 2010 by the American Geophysical Union.

    DOI: 10.1029/2010JA015848

    Scopus

  302. Calculation of the parameter η krassovsky airglow emissions from the O2 (0-1) and OH (6-2) Reviewed

    Amelia Naomi Onohara, Hisao Takahashi, Delano Gobbi, Kazuo Shiokawa

    Revista Brasileira de Geofisica   Vol. 28 ( 4 ) page: 579 - 592   2010

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    Language:Portuguese   Publishing type:Research paper (scientific journal)   Publisher:Sociedade Brasileira de Geofisica  

    In this work, the Krassovsky's η parameter, was used to investigate the amplitudes and phases of periodic variations of O2(0-1) and OH(6-2) airglow emissions. The data set was obtained from photometer measurements at Rikubetsu (43.5°N, 143.8°E), Japan, from March 2004 to August 2005, under collaboration with STEL-LAB (Solar-Terrestrial Environment Laboratory), Nagoya University. The results showed |η| = 5.3 ± 1.7 and Φ = -40.2°± 30.6° for O2 emission, and {pipe}η{pipe} = 8.0 ± 4.7 and Φ = -41.9°± 41.4° for OH emission. There is a good agreement between the results obtained in this work with the previous results. But, it must be emphasized that the models for Φ don't predict the results as good as the models for |η|. It was found the existence of larger |η| values for the OH emission, so that there are few results in literature concerning of this high values. Comparing it with the models of Schubert et al. (1991), it was observed that they have good correlation with the model for a gravity wave with a horizontal wavelength of 100 km. © 2010 Sociedade Brasileira de Geofísica.

    DOI: 10.1590/S0102-261X2010000400004

    Scopus

  303. Lower-thermospheric wind fluctuations measured with an FPI during pulsating aurora at Tromso, Norway Reviewed

    S. Oyama, K. Shiokawa, J. Kurihara, T. T. Tsuda, S. Nozawa, Y. Ogawa, Y. Otsuka, B. J. Watkins

    ANNALES GEOPHYSICAE   Vol. 28 ( 10 ) page: 1847 - 1857   2010

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:COPERNICUS GESELLSCHAFT MBH  

    Simultaneous observations were conducted with a Fabry-Perot Interferometer (FPI) at a wavelength of 557.7 nm, an all-sky camera at a wavelength of 557.7 nm, and the European Incoherent Scatter (EISCAT) UHF radar during the Dynamics and Energetics of the Lower Thermosphere in Aurora 2 (DELTA-2) campaign in January 2009. This paper concentrated on two events during periods of pulsating aurora. The lower-thermospheric wind velocity measured with the FPI showed obvious fluctuations in both vertical and horizontal components. Of particular interest is that the location of the fluctuations was found in a darker area that appeared within the pulsating aurora. During the same time period, the EISCAT radar observed sporadic enhancements in the F-region backscatter echo power, which suggests the presence of low-energy electron (1 keV or lower) precipitation coinciding with increase in amplitude of the electromagnetic wave (at the order of 10 Hz or higher). While we have not yet identified the dominant mechanism causing the fluctuations in FPI-derived wind velocity during the pulsating aurora, the frictional heating energy dissipated by the electric-field perturbations may be responsible for the increase in ionospheric thermal energy thus modifying the local wind dynamics in the lower thermosphere.

    DOI: 10.5194/angeo-28-1847-2010

    Web of Science

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  304. Simultaneous FAST and Double Star TC1 observations of broadband electrons during a storm time substorm Reviewed

    Nakajima A.

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 7 )   2010

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    Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research: Space Physics  

    DOI: 10.1029/2009JA014907

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  305. Simultaneous FAST and Double Star TC1 observations of broadband electrons during a storm time substorm Reviewed

    A. Nakajima, K. Shiokawa, K. Seki, R. Nakamura, K. Keika, W. Baumjohann, T. Takada, J. P. McFadden, C. W. Carlson, A. N. Fazakerley, H. Rème, I. Dandouras, R. J. Strangeway, O. Le Contel, N. Cornilleau-Wehrlin, K. H. Yearby

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 7 )   2010

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

    Broadband electrons (BBEs) exhibit remarkable electron flux enhancements over a broad energy range (0.03-30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. Here, we report a BBE event observed by the Fast Auroral Snapshot (FAST) satellite at 1355-1359 UT, ∼61-66 invariant latitudes, ∼0600 magnetic local time (MLT), and ∼3800 km altitude during a storm on 25 July 2004. The Double Star (DS) TC1 satellite was located near the magnetic equator at L = 5.7, close to the same local time as FAST. We investigate the acceleration process of BBEs from the inner magnetosphere to near the ionosphere by comparing electron data obtained by FAST and DS TC1. We also investigate both plasma and field variations in the inner magnetosphere associated with substorm onset using DS TC1 data to examine the relationship between the BBEs and the storm time substorm. Ground geomagnetic field data show a positive H-bay at ∼1349 UT at ∼0600 MLT, indicating that a storm time substorm started just before the appearance of the BBEs. At ∼1350 UT, a tailward ion flow was observed by DS TC1. Then, DS TC1 observed a local dipolarization and a drastic ion density enhancement at ∼1351 UT, indicating that particle heating associated with the substorm was occurring in the inner magnetosphere. From ∼1352 UT, electron fluxes were isotropically enhanced at energies above ∼0.5 keV as observed by DS TC1. On the other hand, the pitch angle distribution of BBEs at the FAST altitude showed field-aligned lower-energy electrons below ∼0.5 keV and isotropic higher-energy electrons above ∼0.5 keV. From these data, it was inferred that the BBEs might consist of two energy components due to the acceleration or heating of electrons at different altitudes in association with the storm time substorm. Copyright 2010 by the American Geophysical Union.

    DOI: 10.1029/2009JA014907

    Scopus

  306. Simultaneous airglow, lidar, and radar measurements of mesospheric gravity waves over Japan Reviewed

    S. Suzuki, T. Nakamura, M. K. Ejiri, M. Tsutsumi, K. Shiokawa, T. D. Kawahara

    Journal of Geophysical Research Atmospheres   Vol. 115 ( 24 )   2010

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

    To investigate gravity wave dynamics in the mesosphere and lower thermosphere (MLT) region, we conducted coordinated observations of mesospheric gravity waves over Japan during the Aeronomy and Dynamics Observation campaign. Two all-sky airglow imagers were used in this campaign to derive a two-dimensional structure of the gravity waves
    these imagers were installed at the middle and upper atmosphere (MU) observatory in Shigaraki (34.9°N, 136.1°E) and at the Dynic Astropark Observatory in Taga (35.2°N, 136.3°E). Simultaneous measurements of the horizontal winds and the temperature in the MLT region were provided by the meteor-mode observations of the MU radar at Shigaraki and by a sodium temperature lidar at Uji (34.9°N, 135.8°E), respectively. On 2 October 2008, gravity waves having a horizontal wavelength of ∼170 km, wave period of ∼1 h, and propagating northeastward at ∼50 m s&lt
    sup&gt
    -1&lt
    /sup&gt
    were observed in the airglow keograms. Similar wave structures were observed in the time series of the meteor wind and lidar temperature data
    the polarity of these waves varied consistently with the airglow intensity variations according to the linear theory of gravity waves. The phase speeds and momentum fluxes of the gravity waves, estimated from the wind and temperature observations, were also in good agreement with those obtained from the airglow measurements. These results demonstrate, both qualitatively and quantitatively, that an identical gravity wave structure was detected in all the airglow intensities, radar winds, and lidar temperature. Copyright 2010 by the American Geophysical Union.

    DOI: 10.1029/2010JD014674

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  307. Simultaneous airglow, lidar, and radar measurements of mesospheric gravity waves over Japan Reviewed

    Suzuki S.

    Journal of Geophysical Research Atmospheres   Vol. 115 ( 24 )   2010

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    Publishing type:Research paper (scientific journal)   Publisher:Journal of Geophysical Research Atmospheres  

    DOI: 10.1029/2010JD014674

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  308. Reorganization of polar cap patches through shears in the background plasma convection Reviewed

    K. Hosokawa, J. P. St-Maurice, G. J. Sofko, K. Shiokawa, Y. Otsuka, T. Ogawa

    Journal of Geophysical Research: Space Physics   Vol. 115 ( 1 )   2010

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

    On the night of December 20, 2006, 630 nm airglow images obtained by an all-sky camera at Resolute Bay, Canada (74.73°N, 265.07°E
    altitude adjusted corrected geomagnetic (AACGM) latitude 82.9°) showed the passage of successive polar cap patches. Shortly after convection came to a temporary halt, one of the patches was reorganized into two substructures in approximately 8 min. The two-dimensional background ionospheric convection pattern measured using the newly deployed PolarDARN radar at Rankin Inlet (62.82°N, 93.11°W
    AACGM latitude 72.96°) showed that a velocity shear of approximately 120 m s-1/340 km suddenly appeared in the vicinity of the patch at the time of reorganization. A qualitative analysis of the relationship between the magnitude of the velocity shear and the distance between the divided patches indicates that the shear in the background plasma convection velocity significantly contributed to the reorganization of the patch. This shear structure appeared soon after a southward turning of the interplanetary magnetic field (IMF) and was probably associated with the reconfiguration of the convection pattern from a pre-existing northward-oriented IMF pattern to a southward-oriented one. The present observations indicate that the reconfiguration/deformation of patches because of a shear in the background convection field, especially reorganization of patches into smaller substructures, may play an important role in the rapid structuring of patches. Copyright 2010 by the American Geophysical Union.

    DOI: 10.1029/2009JA014599

    Scopus

  309. Telescope of Extreme Ultraviolet boarded on KAGUYA: Science from the Moon Reviewed

    Yoshikawa, I, Murakami, G, Ezawa, F, Yoshioka, K, Obana, Y, Taguchi, M, Yamazaki, A, Kameda, S, Nakamura, M, Kikuchi, M, Kagitani, M, Okano, S, Shiokawa, K, Miyake, W

    Advances in Geosciences   Vol. 19   page: 109 - 121   2010

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

    DOI: 10.1142/9789812838162_0009

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  310. Azimuthal structures of ray auroras at the beginning of auroral substorms Reviewed

    K. Sakaguchi, K. Shiokawa, E. Donovan

    GEOPHYSICAL RESEARCH LETTERS   Vol. 36 ( 23 )   2009.12

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    The time evolution of optical structures in brightening auroras was examined for two substorm events that occurred on January 15, 2008 and February 27, 2009. The onsets of both auroral substorms were captured in the field of view of an all-sky TV camera at Gillam, Canada. We found that in both cases, the brightening auroras formed vertical structures, or so-called &apos;ray auroras&apos;, which lined up longitudinally for several tens of seconds before luminosity increased sharply. The ray structure implies precipitating electrons accelerated over a broad energy range at substorm onset. Two dimensional Fourier transform analysis of the auroral images showed the ray auroras have characteristic wavenumbers and harmonics that develop within a few seconds of the initial brightening. These results suggest that dispersive Alfven waves containing turbulent parallel electric fields form in brightening regions at the beginning of auroral substorms. Citation: Sakaguchi, K., K. Shiokawa, and E. Donovan ( 2009), Azimuthal structures of ray auroras at the beginning of auroral substorms, Geophys. Res. Lett., 36, L23106, doi: 10.1029/2009GL041252.

    DOI: 10.1029/2009GL041252

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  311. GPS total electron content variations associated with a polar cap arc Reviewed

    P. T. Jayachandran, K. Hosokawa, J. W. MacDougall, S. Mushini, R. B. Langley, K. Shiokawa

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114 ( 12 )   2009.12

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    We report an example of total electron content (TEC) variations, using Global Positioning System (GPS) measurements, associated with a polar cap arc detected by an all-sky imager and ionosonde at a polar cap station. During the transit of the arc, GPS signals along the arc length showed an increase of similar to 2 TEC units whereas GPS signals perpendicular to the arc showed only an increase of similar to 0.3 TEC units. This indicates that the GPS TEC variations associated with a polar cap arc are dependent on the geometry of the GPS raypaths with respect to the arc. Ionosonde measurements confirm that this arc was an E region feature at similar to 110 km with peak electron density of 5.4 x 10(11) el/m(3). Estimated speed of the arc using a GPS triangulation method was about 300 m/s.

    DOI: 10.1029/2009JA014916

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  312. The Upper Atmosphere and Plasma Imager/the Telescope of Visible Light (UPI/TVIS) onboard the Kaguya spacecraft Reviewed

    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   Vol. 61 ( 12 ) page: xvii-xxiii   2009.12

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  313. Ionospheric and geomagnetic disturbances during the 2005 Sumatran earthquakes Reviewed

    Alina Marie Hasbi, Mohammed Awad Momani, Mohd Alauddin Mohd Ali, Norbahiah Misran, Kazuo Shiokawa, Yuichi Otsuka, Kiyohumi Yumoto

    JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS   Vol. 71 ( 17-18 ) page: 1992 - 2005   2009.12

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    This paper investigates the ionospheric and geomagnetic responses during the 28 March 2005 and 14 May 2005 Sumatran earthquakes using GPS and magnetometer stations located in the near zone of the epicenters. These events occurred during low solar and geomagnetic activity. TEC oscillations with periods of 5-10 min were observed about 10-24 min after the earthquakes and have horizontal propagation velocities of 922-1259 m/s. Ionospheric disturbances were observed at GPS stations located to the northeast of the epicenters, while no significant disturbances were seen relatively east and south of the epicenters. The magnetic field measurements show rapid fluctuations of 4-5 s shortly after the earthquake, followed by a Pc5 pulsation of 4.8 min about 11 min after the event. The correlation between the ionospheric and geomagnetic responses shows a good agreement in the period and time lag of the peak disturbance arrival, i.e. about 11-13 min after the earthquake. (C) 2009 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.jastp.2009.09.004

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  314. Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations Reviewed

    Suzuki S., Shiokawa K., Liu A., Otsuka Y., Ogawa T., Nakamura T.

    Annales Geophysicae   Vol. 27 ( 4 ) page: 1625 - 1629   2009.12

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    We present the characteristics of small-scale (<100 km) gravity waves in the equatorial mesopause region derived from OH airglow imaging observations at Kototabang (100.3° E, 0.2° S), Indonesia, from 2002 to 2005. We adopted a method that could automatically detect gravity waves in the airglow images using two-dimensional cross power spectra of gravity waves. The propagation directions of the waves were likely controlled by zonal filtering due to stratospheric mean winds that show a quasi-biennial oscillation (QBO) and the presence of many wave sources in the troposphere.

    DOI: 10.5194/angeo-27-1625-2009

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  315. Joint observations of a traveling ionospheric disturbance with the Paratunka OMTI camera and the Hokkaido HF radar Reviewed

    Koustov A., Nishitani N., Ponomarenko P.V., Shiokawa K., Suzuki S., Shevtsov B.M., MacDougall J.W.

    Annales Geophysicae   Vol. 27 ( 6 ) page: 2399 - 2406   2009.12

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    On 10 September 2007 between 10:00 and 14:00 UT, the OMTI all-sky imager at Paratunka (Kamchatka, Russia, GLAT∼52°) observed the onset and southwestern progression of a localized depletion region in the airglow intensity. The perturbation, while being stretched in the NW-SE direction, crossed the entire field of view of the camera. During the event, the Hokkaido SuperDARN HF radar was monitoring echoes in the Paratunka longitudinal sector. It was detecting a localized band of ground scatter echoes progressing equatorward synchronously with the motion of the optical perturbation. It is suggested that both features resulted from the onset and south-western progression of a localized region with enhanced electric field that influenced the distribution of the plasma density in the ionosphere. Modeling of the HF ground scatter dynamics based on numerical ray tracing demonstrated qualitative consistency with the observations. © 2009 Author(s).

    DOI: 10.5194/angeo-27-2399-2009

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  316. Effects of geomagnetically induced current on power grids Reviewed

    Watari S., Kunitake M., Kitamura K., Hori T., Kikuchi T., Shiokawa K., Nishitani N., Kataoka R., Kamide Y., Watanabe Y.

    Journal of the National Institute of Information and Communications Technology   Vol. 56 ( 1-4 ) page: 125 - 133   2009.12

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    There have been many reports that geomagnetically induced current (GIC) has affected the operation of electric power grids. Given Japan's location at lower geomagnetic latitude than its geographic latitude, the effects of GIC on electric power grids there are believed to be small, but have yet to be subjected to elaborate analysis. This paper describes the results of GIC measured in Hokkaido over a two-year period in collaboration with the National Institute of Information and Communications Technology (NICT), Hokkaido Electric Power Co., Inc., and the Solar- Terrestrial Environment Laboratory (STEL) of Nagoya University.

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  317. New observational deployments for SEALION-Airglow measurements using all-sky imagers Reviewed

    Kubota M., Ishii M., Tsugawa T., Uemoto J., Jin H., Otsuka Y., Shiokawa K.

    Journal of the National Institute of Information and Communications Technology   Vol. 56 ( 1-4 ) page: 299 - 307   2009.12

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    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.

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  318. Spatial relationship of F-region field-aligned irregularities and medium-scale traveling ionospheric disturbances observed with the MU radar and all-sky airglow imagers Reviewed

    Otsuka Y., Shiokawa K., Ogawa T., Yokoyama T., Yamamoto M.

    ICCAS-SICE 2009 - ICROS-SICE International Joint Conference 2009, Proceedings     page: 1310 - 1311   2009.12

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    We report simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) and field-aligned irregularities (FAIs) in the F region by using two all-sky airglow imagers and the MU radar in Japan. MSTIDs propagating southwestward were observed in 630-nm airglow images on the night of June 16, 2004. During this MSTID event, FAIs in the F region were observed by making multibeam measurements with the MU radar. We found that FAIs with intense (weak) signal-to-noise ratio (SNR) coincided with the airglow depletion (enhancement) caused by the MSTIDs. This result indicates that the FAIs could be generated by the gradient drift instability at the airglow depletion region. © 2009 SICE.

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  319. The optical mesosphere thermosphere imagers (OMTIs) for network measurements of aurora and airglow Reviewed

    Shiokawa K., Hosokawa K., Sakaguchi K., Ieda A., Otsuka Y., Ogawa T., Connors M.

    AIP Conference Proceedings   Vol. 1144   page: 212 - 215   2009.11

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    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 1 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. © 2009 American Institute of Physics.

    DOI: 10.1063/1.3169292

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  320. プラズマバブルに伴うGPSにおけるロック損失分布・全電子数変化率分布の時間変化 Reviewed

    菊地 隼人, 中田 裕之, 津川 卓也, 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 = / Society of Atmospheric Electricity of Japan   Vol. 3 ( 2 ) page: 68-69   2009.10

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  321. Measurements of geomagnetically induced current in a power grid in Hokkaido, Japan Reviewed

    Watari S., Kunitake M., Kitamura K., Hori T., Kikuchi T., Shiokawa K., Nishitani N., Kataoka R., Kamide Y., Aso T., Watanabe Y., Tsuneta Y.

    Space Weather   Vol. 7 ( 3 )   2009.10

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    There have been numerous reports showing that space weather affects power grids through a geomagnetically induced current (GIC). Generally, power grids consist of power lines connected to transformers, of which neutral points are directly grounded. The GIC flows into those transformers through the neutral points if geomagnetic variations cause a ground level potential. These currents can damage power grids, especially transformers. It has been tacitly assumed, however, that the effect of the GIC is minor in Japan because of the country's location at geomagnetically lower latitudes. To examine the GIC effect in Japan, we conducted approximately 2 years of GIC measurements in Hokkaido, Japan. It is found that GICs associated with substorms can be detected in Japan even at the solar minimum although intense GICs do occur mostly during geomagnetic storms. Temporal variations of GICs show high correlation with geomagnetic field variations, rather than time derivatives of the geomagnetic field. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008SW000417

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  322. Spatial relationship of nighttime medium-scale traveling ionospheric disturbances and F region field-aligned irregularities observed with two spaced all-sky airglow imagers and the middle and upper atmosphere radar Reviewed

    Otsuka Y., Shiokawa K., Ogawa T., Yokoyama T., Yamamoto M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114 ( 5 )   2009.5

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    DOI: 10.1029/2008JA013902

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  323. Longitudinal development of a substorm brightening arc Reviewed

    Shiokawa K., Ieda A., Nakajima A., Sakaguchi K., Nomura R., Aslaksen T., Greffen M., Spanswick E., Donovan E., Mende S.B., McFadden J., Glassmeier K.H., Angelopoulos V., Miyashita Y.

    Annales Geophysicae   Vol. 27 ( 5 ) page: 1935 - 1940   2009.5

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    We present simultaneous THEMIS-ground observations of longitudinal (eastward) extension of a substorm initial-brightening arc at Gillam (magnetic latitude: 65.60) at 08:13 UT on 10 January 2008. The speed of the eastward arc extension was ~2.7 km/s. The extension took place very close to the footprints of the longitudinally separated THEMIS E and D satellites at-12 RE. The THEMIS satellites observed field dipolarization, weak earthward flow, and pressure increase, which propagated eastward from E to D at a speed of ~50 km/s. The THEMIS A satellite, located at 1.6 RE earthward of THEMIS E, observed fluctuating magnetic field during and after the dipolarization. The THEMIS E/D observations suggest that the longitudinal extension of the brightening arc at substorm onset is caused by earthward flow braking processes which produce field dipolarization and pressure increase propagating in longitude in the near- earth plasma sheet. © Author(s) 2009.

    DOI: 10.5194/angeo-27-1935-2009

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  324. Motion of polar cap patches: A statistical study with all-sky airglow imager at Resolute Bay, Canada Reviewed

    Hosokawa K., Kashimoto T., Suzuki S., Shiokawa K., Otsuka Y., Ogawa T.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114 ( 4 )   2009.4

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    A highly sensitive all-sky airglow imager (part of the Optical Mesosphere Thermosphere Imagers [OMTIs]) has been operating for 3 years at Resolute Bay, Canada (geographic latitude 74.7°N; geomagnetic latitude 82.9°N) since January 2005. One of its major applications is the observation of polar cap patches. Polar cap patches are generated in the vicinity of the cusp during southward interplanetary magnetic field (IMF) conditions, and they exhibit dynamic movement, possibly in association with the changes in the IMF orientation. In order to determine how their motions are controlled by the upstream IMF conditions, we applied a motion-tracking algorithm that was based on two-dimensional cross-correlation analysis to consecutive images obtained from January 2005 to December 2007 by the all-sky airglow imager at Resolute Bay. We identified and extracted 561 individual patches and then carried out a statistical study of their motion. It is demonstrated that the speed of patches is primarily controlled by the IMF Bz. Furthermore, the dawn-dusk component of the patch drift velocities is well correlated with the IMF B y, which is in good agreement with the published By dependence of the nightside polar cap convection. This enables us to monitor the plasma convection within the polar cap by using polar cap patches as tracers. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008JA014020

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  325. Unusually elongated, bright airglow plume in the polar cap F region: Is it a tongue of ionization? Reviewed

    Hosokawa K., Tsugawa T., Shiokawa K., Otsuka Y., Ogawa T., Hairston M. R.

    GEOPHYSICAL RESEARCH LETTERS   Vol. 36 ( 7 )   2009.4

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    [1] We report an event of unusually elongated, bright airglow plume, which is considered as an optical manifestation of tongue of ionization (TOI) in the central polar cap. This optical structure was detected with an all-sky airglow imager at Resolute Bay (74.73°N, 265.07°E) during a large magnetic storm on December 15, 2006. The absolute optical intensity of the plume was ≈ kR, which is much brighter than that of non-stormtime polar cap patches. Two-dimensional imaging capability of the all-sky imager demonstrates that some meso-scale structures (≈250-600 km) were embedded within the plume. Simultaneous ion density and drift measurements with the DMSP spacecraft strongly suggest that the plume was extending from the dayside as a narrow stream of dense plasma and thus is an optical manifestation of polar cap TOI. The DMSP data also implies that the possible source of the plume is a narrow stream of storm enhanced density (SED) transported from lower latitudes. The DMSP auroral particle observation demonstrates that the polar cap extremely expanded equatorward during this interval. This extreme expansion allowed the anti-sunward convection to capture plasmas within the SED and deliver them deep into the polar cap as a luminous airglow plume. This observation claims that the plasma transport from the dayside lower latitudes plays an important role in controlling the plasma environment in the polar cap ionosphere during magnetic storms. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2009GL037512

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  326. Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below Reviewed

    Ogawa Tadahiko, Miyoshi Yasunobu, Otsuka Yuichi, NAKAMURA Takuji, SHIOKAWA Kazuo

    Earth, planets and space   Vol. 61 ( 4 ) page: 397-410   2009.4

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  327. Possible influence of ultra-fast Kelvin wave on the equatorial ionosphere evening uplifting Reviewed

    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   Vol. 61 ( 4 ) page: 455-462   2009.4

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  328. Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes Reviewed

    Shiokawa K., Otsuka Y., Ogawa T.

    Earth, planets and space   Vol. 61 ( 4 ) page: 479-491   2009.4

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  329. Medium-scale traveling ionospheric disturbances observed with the SuperDARN Hokkaido radar, all-sky imager, and GPS network and their relation to concurrent sporadic E irregularities Reviewed

    Ogawa T., Nishitani N., Otsuka Y., Shiokawa K., Tsugawa T., Hosokawa K.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114 ( 3 )   2009.3

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    We present midlatitude medium-scale traveling ionospheric disturbances (MSTIDs) observed with a Super Dual Auroral Radar Network (SuperDARN) HF radar at around 10 MHz in Hokkaido, Japan, in combination with a 630-nm all-sky imager and a GPS network (GEONET) that provides total electron content (TEC) data. MSTIDs propagating southward from high latitudes are detected at first with the HF radar and then with the imager and GEONET. We analyze two MSTID events, one in winter (event 1) and the other in summer (event 2), to find that MSTIDs appear simultaneously, at least, at 55°-25°N. It is shown that nighttime MSTIDs propagate toward the southwest over a horizontal distance of about 4000 km, and daytime MSTIDs do so toward the southeast. Daytime radar echoes are due to ground/sea surface (GS) scatter, while nighttime echoes in event 1 return from 15-m-scale F region field-aligned irregularities (FAIs) and those in event 2 are due to GS scatter. Doppler velocities of the nighttime F region FAI echoes in event 1 are negative (motion away from the radar) within strong echo regions and are positive (motion toward the radar) within weak echo regions. This fact suggests that the strong (weak) echoes return from suppressed (enhanced) airglow/TEC areas, in line with previous observations over central Japan. The nighttime MSTIDs in events 1 and 2 are often accompanied by concurrent coherent echoes from FAIs in sporadic E (Es) layers. The Es echo areas in event 2 rather coincide with suppressed airglow/TEC areas in the F region that are connected with the echo areas along the geomagnetic field, indicating the existence of E and F region coupling at night. Copyright 2009 by the American Geophysical Union.

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  330. Super plasma fountain and equatorial ionization anomaly during penetration electric field Reviewed

    Balan N., Shiokawa K., Otsuka Y., Watanabe S., Bailey G. J.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114 ( 3 )   2009.3

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    DOI: 10.1029/2008JA013768

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  331. Relationship between polar cap patches and field-aligned irregularities as observed with an all-sky airglow imager at Resolute Bay and the PolarDARN radar at Rankin Inlet Reviewed

    Hosokawa K., Shiokawa K., Otsuka Y., Ogawa T., St-Maurice J. -P., Sofko G. J., Andre D. A.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114 ( 3 )   2009.3

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    Simultaneous two-dimensional observations of airglow enhancement and radar backscatter from field-aligned irregularities (FAIs) associated with polar cap patches were conducted. The spatial structure of 630 nm airglow from polar cap patches was imaged using an all-sky airglow imager at Resolute Bay, Canada, while backscatter echoes from decameter-scale FAIs were observed using the newly constructed HF Polar Dual Auroral Radar Network (PolarDARN) radar at Rankin Inlet, Canada. Both the airglow enhancement and the radar backscatter appeared within a structured region with the spatial extent of about 500-1000 km. The decameter-scale FAIs were found to extend over the entire region of airglow enhancement associated with polar cap patches, indicating that the polar patch plasma became almost fully structured soon after initiation (within approximately 2025 min). These findings imply that some rapid structuring process of the entire patch area is involved in addition to the primary gradient-drift instabilities. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008JA013707

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  332. 赤道プラズマバブルに伴うGPSでのロック損失と全電子数変化率分布 Reviewed

    菊地 隼人, 中田 裕之, 津川 卓也, 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 = / Society of Atmospheric Electricity of Japan   Vol. 3 ( 1 ) page: 126-127   2009.3

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  333. Effects observed in the ionospheric F region in the east Asian sector during the intense geomagnetic disturbances in the early part of November 2004 Reviewed

    Sahai Y., Becker-Guedes F., Fagundes P.R., De Jesus R., De Abreu A.J., Otsuka Y., Shiokawa K., Igarashi K., Yumoto K., Huang C.S., Lan H.T., Saito A., Guarnieri F.L., Pillat V.G., Bittencourt J.A.

    Journal of Geophysical Research: Space Physics   Vol. 114 ( 3 )   2009.3

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    The Sun was very active in the early part of November 2004. During the period of 8-10 November 2004, intense geomagnetic disturbances with two superstorms were observed. In a companion paper (hereinafter referred to as paper 1), the effects observed in the F region during the intense geomagnetic disturbances in the early part of November 2004 in the Latin American sector were presented. In the present paper, we investigate the effects observed in the F region during the intense geomagnetic disturbances in the early part of November 2004 in the east Asian sector. We have used the ionospheric sounding observations at Ho Chi Minh City (Vietnam) and Okinawa, Yamagawa, Kokubunji, and Wakkanai (Japan) in the present investigations. Also, GPS observations in the east Asian sector (several longitude zones) have been used to study the effect in the F region during the intense geomagnetic disturbances. The ion density versus latitudinal variations obtained by the DMSP F15 satellite orbiting at about 800 km altitude in the east Asian sector and the magnetic field data obtained at several stations in the Japanese meridian are also presented. Several important features from these observations in both the sectors during this extended period of intense geomagnetic disturbances are presented. The east Asian sector showed very pronounced effects during the second superstorm, which was preceded by two storm enhancements. It should be mentioned that around the beginning of the night on 10 November, ionospheric irregularities propagating from higher midlatitude region to low-latitude region were observed in the Japanese sector. The most intense geomagnetic field H component in that sector was observed on 10 November at L = 2.8, indicating that the auroral oval and the heating got further to low latitudes and the ionospheric irregularities observed in the Japanese sector on this night are midlatitude ionospheric disturbances associated with the second superstorm. The absence of ionospheric irregularities in the Japanese sector during the 8 November superstorm suggests that the magnetosphere-ionosphere system was possibly preconditioned (primed) when the second interplanetary structure impacted the magnetosphere. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008JA013053

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  334. Fine structures and dynamics in auroral initial brightening at substorm onsets Reviewed

    Sakaguchi K., Shiokawa K., Ieda A., Nomura R., Nakajima A., Greffen M., Donovan E., Mann I., Kim H., Lessard M.

    Annales Geophysicae   Vol. 27 ( 2 ) page: 623 - 630   2009.2

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    We show four auroral initial brightening events at substorm onsets focusing on fine structures and their longitudinal dynamics, which were observed by all-sky TV cameras (30-Hz sampling) on January 2008, in Canada. For two initial brightenings started in the field of views of the cameras, we found that they started at longitudinal segments with a size of less than ∼30g-60 km. One brightening expanded with wavy structures and the other expanded as a straight arc. Although the two events had different structures, both brightening auroras expanded with an average speed of ∼20 km/s in the first 10 s, and ∼10 km/s in the following 10 s. The other two events show that brightening auroras developed with periodic structures, with longitudinal wavelengths of ∼100g-200 km. Assuming that the brightening auroras are mapped to the physical processes occurring in the plasma sheet, we found that the scale size (30g-60 km) and the expanding speed (20 km/s) of brightening auroras correspond to the order of ion gyro radii (∼500g-1400 km) and Alfvén speed or fast ion-flow speed (∼400 km/s), respectively, in the plasma sheet.

    DOI: 10.5194/angeo-27-623-2009

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  335. Medium-Scale Traveling Ionospheric Disturbances and Plasma Bubbles Observed by an All-Sky Airglow Imager at Yonaguni, Japan Reviewed

    Ogawa Tadahiko, Otsuka Yuichi, Shiokawa Kazuo, Tsugawa Takuya, Saito Akinori, Hoshinoo Kazuaki, Matunaga Keisuke, Kubota Minoru, Ishii Mamoru

    TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES   Vol. 20 ( 1 ) page: 287 - 295   2009.2

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    DOI: 10.3319/TAO.2007.12.06.02(F3C)

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  336. Statistical characteristics of polar cap mesospheric gravity waves observed by an all-sky airglow imager at Resolute Bay, Canada Reviewed

    Suzuki S., Shiokawa K., Hosokawa K., Nakamura K., Hocking W. K.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 114 ( 1 )   2009.1

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    DOI: 10.1029/2008JA013652

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  337. The Optical Mesosphere Thermosphere Imagers (OMTIs) for network measurements of aurora and airglow Reviewed

    Shiokawa, K., K. Hosokawa, K. Sakaguchi, A. Ieda, Y. Otsuka, T. Ogawa and M. Connors

    Future Perspectives of Space Plasma and Particle Instrumentation and International Collaborations, AIP Conference proceedings, edited by M. Hirahara, Y. Miyoshi, N. Terada, I. Shinohara,and T. Mukai, AIP Conference proceedings     page: 212-215, doi:10.1063/1.3169292   2009

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  338. Longitudinal development of a substorm brightening arc Reviewed

    Shiokawa, K., A. Ieda, A. Nakajima, K. Sakaguchi, R. Nomura, T. Aslaksen, M. Greffen, E. Spanswick, and E. Donovan, S. B. Mende, J. McFadden, K.-H. Glassmeier, V. Angelopoulos, and Y. Miyashita

    Ann. Geophys.   Vol. 27   page: 1935-1940   2009

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  339. *Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes Reviewed

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

    Earth Planets Space   Vol. 61   page: 479-491   2009

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    We review measurements of nighttime atmospheric/ionospheric waves 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 hydroxyl (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, ~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. Poleward-propagating waves tend to be observed in the summer in the mesopause region at several stations, suggesting that mesospheric gravity waves are generated by intense convective activity in the equatorial 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 region 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.

  340. Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below Reviewed

    Ogawa Tadahiko, Miyoshi Yasunobu, Otsuka Yuichi, Nakamura Takuji, Shiokawa Kazuo

    EARTH PLANETS AND SPACE   Vol. 61 ( 4 ) page: 397 - 410   2009

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  341. Fine structures and dynamics in auroral initial brightening at substorm onsets Reviewed

    Sakaguchi K., Shiokawa K., Ieda A., Nomura R., Nakajima A., Greffen M., Donovan E., Mann I. R., Kim H., Lessard M.

    ANNALES GEOPHYSICAE   Vol. 27 ( 2 ) page: 623-630   2009

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  342. The Optical Mesosphere Thermosphere Imagers (OMTIs) for network measurements of aurora and airglow Reviewed

    Shiokawa K., Hosokawa K., Sakaguchi K., Ieda A., Otsuka Y., Ogawa T., Connors M.

    FUTURE PERSPECTIVES OF SPACE PLASMA AND PARTICLE INSTRUMENTATION AND INTERNATIONAL COLLABORATIONS   Vol. 1144   page: 212-+   2009

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  343. Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes Reviewed

    Shiokawa K., Otsuka Y., Ogawa T.

    EARTH PLANETS AND SPACE   Vol. 61 ( 4 ) page: 479-491   2009

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  344. 28pSP-16 Precipitation of radiation belt relativistic electrons by electromagnetic ion cyclotron waves Reviewed

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

    Meeting Abstracts of the Physical Society of Japan   Vol. 64 ( 0 )   2009

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    DOI: 10.11316/jpsgaiyo.64.1.2.0_228_1

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  345. Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations Reviewed

    Suzuki S., Shiokawa K., Liu A. Z., Otsuka Y., Ogawa T., Nakamura T.

    ANNALES GEOPHYSICAE   Vol. 27 ( 4 ) page: 1625 - 1629   2009

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  346. Joint observations of a traveling ionospheric disturbance with the Paratunka OMTI camera and the Hokkaido HF radar Reviewed

    Koustov A., Nishitani N., Ponomarenko P. V., Shiokawa K., Suzuki S., Shevtsov B. M., MacDougall J. W.

    ANNALES GEOPHYSICAE   Vol. 27 ( 6 ) page: 2399 - 2406   2009

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  347. Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below Reviewed

    Ogawa T., Miyoshi Y., Otsuka Y., Nakamura T., Shiokawa K.

    Earth, Planets and Space   Vol. 61 ( 4 ) page: 397 - 410   2009

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    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 0100 LT in equinoctial months with a seasonal asymmetry, and their activity decreases with decreasing solar activity. A comparison between scintillation index (S4) and Earth's brightness temperature (Tbb) variations suggests that the scintillation activity can be related to tropospheric disturbances over the Indian Ocean to the west of Kototabang. To understand better the reasons of day-to-day variability of S4, we analyze S4, rbb and lower thermospheric neutral wind (u′2̄) data. The results show that 54 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 Tbb and u′2̄ 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 a whole, move eastward at about 100-1 while changing patterns over time. These simulations suggest that the Rayleigh-Taylor instability responsible for plasma bubble generation can 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 from below. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

    DOI: 10.1186/BF03353157

    Scopus

  348. Coordinated observations of nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow and HF radar echoes at midlatitudes Reviewed

    Suzuki S., Hosokawa K., Otsuka Y., Shiokawa K., Ogawa T., Nishitani N., Shibata T.F., Koustov A.V., Shevtsov B.M.

    Journal of Geophysical Research: Space Physics   Vol. 114 ( 7 )   2009

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    We investigate nighttime medium-scale traveling ionospheric disturbances (MSTIDs) using the SuperDARN HF radar at Hokkaido, Japan (43.5°N, 143.6°E), and an OI 630-nm airglow imager located at Paratunka, Russia (53.0°N, 158.2°E), within the radar field of view. The imager identified southwestward propagating MSTIDs with a horizontal wavelength of ∼300 km on 8 December 2007. Throughout this event, the radar continuously detected ionospheric echoes originating from decameter-scale field-aligned irregularities (FAIs) at the F region heights. The Doppler velocities of these echoes showed systematic polarity changes which were consistent with airglow intensity variations. These polarity changes would be attributed to E × B plasma drifts caused by the polarization electric field embedded in the MSTIDs. The FAI echo powers also varied in agreement with the airglow intensity variations: strong (weak) echoes coincided with the airglow depletion (enhancement) region. Considering the MSTID polarization electric field, it is suggested that the observed FAIs were generated by the gradient drift instability on the bottomside of the F region. Copyright 2009 by the American Geophysical Union.

    DOI: 10.1029/2008JA013963

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  349. Possible influence of ultra-fast Kelvin wave on the equatorial ionosphere evening uplifting Reviewed

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

    Earth, Planets and Space   Vol. 61 ( 4 ) page: 455 - 462   2009

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    Equatorial 3.5-day ultra-fast Kelvin wave was observed in the MLT zonal wind measured by meteor radar at Cariri (7.4°S, 36.5°W, geomag. 8°S) and in the stratosphere-mesosphere temperature structures from the TIMED/SABER data. The ionospheric F-layer bottom-side virtual height h'F and the critical frequency. F0F2 Observed at Fortaleza (3.9°S, 38.4°W, Geomag. 5°S) Also Showed Similar Oscillation Structures, Indicating An Influence of the Kelvin Wave in the F Region Height and Modulation of e X B Uplifting during the Evening Period. Consequently the Ionospheric Spread F Onset Time Was Also Modulated in the Same Period, Around 4 Days. Copyright © the Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

    DOI: 10.1186/BF03353162

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  350. Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes Reviewed

    Shiokawa K., Otsuka Y., Ogawa T.

    Earth, Planets and Space   Vol. 61 ( 4 ) page: 479 - 491   2009

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Earth, Planets and Space  

    We review measurements of nighttime atmospheric/ionospheric waves 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 hydroxyl (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, ~ 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. Poleward-propagating waves tend to be observed in the summer in the mesopause region at several stations, suggesting that mesospheric gravity waves are generated by intense convective activity in the equatorial 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 region 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. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sci enees (SGEPSS).

    DOI: 10.1186/BF03353165

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  351. The upper atmosphere and plasma imager/the telescope of visible light (UPI/TVIS) onboard the kaguya spacecraft Reviewed

    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   Vol. 61 ( 12 )   2009

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    The Upper Atmosphere and Plasma Imager (UPI) was placed in a lunar orbit in order to study both the Moon and Earth. The UPI consists of two telescopes: a Telescope of Extreme Ultraviolet (TEX) and a Telescope of Visible Light (TVIS), which are both mounted on a two-axis gimbals system. The TVIS is equipped with fast catadioptric optics and a high-sensitivity CCD to image swift aurora and dark airglow in the terrestrial upper atmosphere. TVIS has a field-of-view equivalent to the Earth's disk as seen from the Moon. The spatial resolution is about 30 km × 70 km on the Earth's surface at auroral latitudes. The observation wavelengths can be changed by selecting different bandpass filters. Using the images of the northern and southern auroral ovals taken by TVIS, the intensities and shapes of the conjugate auroras will be quantitatively compared. Using the airglow imaging, medium- and large-scale ionospheric disturbances will be studied. In this paper, the instrumental design and performance of TVIS are presented.copyright © the society of geomagnetism and earth, planetary and space science.

    DOI: 10.1186/BF03352980

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  352. ULF geomagnetic anomalous changes possibly associated with 2004-2005 Sumatra earthquakes Reviewed

    Saroso S., Hattori K., Ishikawa H., Ida Y., Shirogane R., Hayakawa M., Yumoto K., Shiokawa K., Nishihashi M.

    Physics and Chemistry of the Earth   Vol. 34 ( 6-7 ) page: 343 - 349   2009

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    Anomalous ULF geomagnetic field change is considered to be one of the most convincing and promising phenomena among earthquake-related electromagnetic effects, because we expect emissions from the crust of the source region. There has been a great deal of accumulated and convincing evidence of ULF magnetic signatures before large earthquakes as reported in the previous studies. In order to verify these phenomena preceding large earthquakes and to clarify the relationship between electromagnetic phenomena and possible physical mechanism, we have investigated the data of ULF geomagnetic observations at Kototabang and Biak stations associated with the 2004/2005 Sumatra earthquakes. A case study is carried out in this work to investigate the pre-earthquake ULF geomagnetic anomalies during the Sumatra-Andaman earthquake on December 26, 2004 (magnitude Mw = 9.0 and depth = 30 km from USGS catalog), and Sumatra-Nias earthquake on March 28, 2005 (Mw = 8.7 and depth = 30 km). For the aim of finding any precursors, we have adopted the spectral density ratio analysis and transfer functions analysis based on wavelet transform method. Results of the spectral density analysis indicate similar variations to those of amplitude for the induction arrow in transfer function analysis. Both of these variations at Kototabang exhibit strange or anomalous changes from a few weeks before the Sumatra-Andaman earthquake to July 2005, while there are no apparent changes at remote station of Biak. To make these results more convincing, the fractal analysis based on a Higuchi method has been applied to the same observed data, which also show a significant change (or decrease) in mono-fractal dimension a few weeks before the earthquakes. This result would lend a further support to those by the spectral density ratio and transfer function analyses. So, we can conclude that the anomalous change as observed simultaneously by the three methods, might be a possible signature related with the earthquake preparation phase of Sumatra earthquakes. © 2008 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.pce.2008.10.065

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

    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   Vol. 113 ( A12 )   2008.12

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    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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  354. Precipitation of radiation belt electrons by EMIC waves, observed from ground and space Reviewed

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

    GEOPHYSICAL RESEARCH LETTERS   Vol. 35 ( 23 )   2008.12

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    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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  355. Correlation of substorm injections, auroral modulations, and ground Pi2 Reviewed

    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   Vol. 35 ( 17 )   2008.9

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    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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  356. Simultaneous THEMIS in situ and auroral observations of a small substorm Reviewed

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

    Geophysical Research Letters   Vol. 35 ( 17 )   2008.9

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    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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  357. Rankin Inlet PolarDARN radar observations of duskward moving Sun-aligned optical forms Reviewed

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

    Annales Geophysicae   Vol. 26 ( 9 ) page: 2711 - 2723   2008.9

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    On 15 February 2007, several duskward moving sun-aligned (SA) auroral forms have been observed by the all-sky camera at Resolute Bay, Nunavut (Canada). Concurrent observations with the Rankin Inlet (RANK) PolarDARN HF radar within the field-of-view of the camera showed signatures of moving auroral forms in all signal parameters with the most remarkable effects being the echo power drop and velocity reversal as the arc reached a specific radar beam/gate. Spatial and temporal variations of the velocity in the vicinity of the SA form are investigated. It is shown that the form-associated convection reversal was located poleward (duskward) of the global-scale convection reversal associated with the dawn cell of the large-scale convection pattern. Thus, the RANK radar was monitoring the polar cap portion of the global-scale convection pattern and its transition from the IMF By&lt;0 to the By&gt;0 situation. Magnetic perturbations associated with the SA form passing the zenith of several magnetometers are investigated. It is shown that although magnetometer signatures of the moving form were clear, the convection pattern derivation from magnetometer records alone is not straightforward.

    DOI: 10.5194/angeo-26-2711-2008

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  358. Development of an automatic procedure to estimate the reflection height of tweek atmospherics Reviewed

    Ohya Hiroyo, Shiokawa Kazuo, Miyoshi Yoshizumi

    Earth, planets and space   Vol. 60 ( 8 ) page: 837-843   2008.8

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  359. Particle and field characteristics of broadband electrons observed by the FAST satellite during geomagnetic storms: A multievent study Reviewed

    Nakajima A., Shiokawa K., Seki K., McFadden J. P., Carlson C. W., Strangeway R. J., Yumoto K.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 113 ( A6 )   2008.6

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher: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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  360. プラズマバブルの発生位置の同定 Reviewed

    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   Vol. 2 ( 1 ) page: 147-148   2008.5

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  361. Simultaneous appearance of isolated auroral arcs and Pc 1 geomagnetic pulsations at subauroral latitudes Reviewed

    Sakaguchi K., Shiokawa K., Miyoshi Y., Otsuka Y., Ogawa T., Asamura K., Connors M.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 113 ( A5 )   2008.5

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    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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  362. Atmospheric gravity waves identified by ground-based observations of the intensity and rotational temperature of OH airglow Reviewed

    Suzuki Hidehiko, Shiokawa Kazuo, Tsutsumi Masaki, Nakamura Takuji, Taguchi Makoto

    Polar science   Vol. 2 ( 1 ) page: 1-8   2008.3

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  363. Atmospheric gravity waves identified by ground-based observations of the intensity and rotational temperature of OH airglow Reviewed

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

    Polar Science   Vol. 2 ( 1 ) page: 1 - 8   2008.3

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher: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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  364. Optical and radio observations and AMIE/TIEGCM modeling of nighttime traveling ionospheric disturbances at mid-latitudes during geomagnetic storms Reviewed

    Shiokawa, K., T. Tsugawa, Y. Otsuka, T. Ogawa, G. Lu, A. Saito, and M. Yamamoto

    AGU monograph on Mid-Latitude Ionospheric Dynamics and Disturbances     page: 271-281   2008

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

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

    J. Geophys. Res   Vol. 113 ( A12312 ) page: doi:10.1029/2008JA013417   2008

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  366. Development of an automatic procedure to estimate the reflection height of tweek atmospherics Reviewed

    Ohya Hiroyo, Shiokawa Kazuo, Miyoshi Yoshizumi

    EARTH PLANETS AND SPACE   Vol. 60 ( 8 ) page: 837 - 843   2008

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  367. Rankin Inlet PolarDARN radar observations of duskward moving Sun-aligned optical forms Reviewed

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

    ANNALES GEOPHYSICAE   Vol. 26 ( 9 ) page: 2711-2723   2008

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  368. Development of an automatic procedure to estimate the reflection height of tweek atmospherics Reviewed

    Ohya H., Shiokawa K., Miyoshi Y.

    Earth, Planets and Space   Vol. 60 ( 8 ) page: 837 - 843   2008

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Earth, Planets and Space  

    This paper presents an automated procedure to estimate apparent reflection height h (from the cutoff frequency for the first waveguide mode, fc), horizontal propagation distance d, and propagation time Tg of tweek atmospherics. Tweek data recorded at the Kagoshima Observatory (31.48°N, 130.72°E), Japan, were used to evaluate the procedure by comparing the results estimated by the automatic method to those read manually by an operator. The two types of results showed differences (automatic-manual) of +0.58 km, -9.9 Hz, and +3058.9 km for mean h, fc, and d, respectively. The difference in h (fc) was less than the resolution of the fast Fourier transform used to obtain the tweek spectra. These comparisons indicate that the automatic estimation procedure of tweek parameters developed in this paper performs well and is a useful tool for studying long-term height variations of the ionospheric D and lower E regions using very low frequency (VLF) and extremely low frequency (ELF) records observed in Japan over the past 30 years. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB.

    DOI: 10.1186/BF03352835

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

    Shiokawa K., Tsugawa T., Otsuka Y., Ogawa T., Lu G., Saito A., Yamamoto M.

    MIDLATITUDE IONOSPHERIC DYNAMICS AND DISTURBANCES   Vol. 181   page: 271 - 281   2008

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:Geophysical Monograph Series  

    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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  370. Simultaneous observations of nighttime medium-scale traveling ionospheric disturbances and E region field-aligned irregularities at midlatitude Reviewed

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

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 112 ( A6 )   2007.6

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

    DOI: 10.1029/2005JA011548

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  371. Signatures of ultra fas Kelvin waves in the equatorial middle atmosphere and ionosphere Reviewed

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

    Geophysical Research Letters   Vol. 34 ( 11 )   2007.6

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    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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  372. Particle and field characteristics of broadband electrons observed by the FAST satellite during a geomagnetic storm Reviewed

    Nakajima A., Shiokawa K., Seki K., Strangeway R. J., McFadden J. P., Carlson C. W.

    JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS   Vol. 112 ( A6 )   2007.6

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher: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 fiel