研究者詳細 - 西谷　望

論文 - 西谷　望

分割表示 >> ／全件表示 96 件中 1 - 96 件目

Multi-Event Analysis of STEVE, SAR Arc, and Red/Green Arc at Subauroral Latitudes Using Data From Ground Optical and Radio Instruments and the Arase and Van Allen Probes Satellites

Sugimura, R; Shiokawa, K; Otsuka, Y; Oyama, S; Oksanen, A; Connors, M; Kadokura, A; Poddelsky, I; Nishitani, N; Shepherd, SG; Ruohoniemi, JM; Smith, C; Spence, H; Reeves, G; Funsten, HO; Miyoshi, Y; Shinohara, I; Kasahara, Y; Tsuchiya, F; Kumamoto, A; Shinbori, A; Asamura, K; Yokota, S; Kazama, Y; Jun, CW; Wang, SY; Tam, SWY; Chang, TF; Wang, BJ; Kasahara, S; Keika, K; Hori, T; Matsuoka, A

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 130 巻 ( 2 ) 2025年2月

Auroral and Magnetotail Dynamics During Quiet-Time STEVE and SAID

Nishimura, Y; Gallardo-Lacourt, B; Donovan, EF; Angelopoulos, V; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 129 巻 ( 11 ) 2024年11月

Polarization and <i>m</i>-Number Characteristics of Mid-Latitude Pc5 ULF Waves Observed by SuperDARN Radars

Morita, K; Ponomarenko, P; Nishitani, N; Hori, T; Shepherd, SG

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 129 巻 ( 9 ) 2024年9月

Obtaining Continental-Scale, High-Resolution 2-D Ionospheric Flows and Application to Meso-Scale Flow Science

Nishimura, Y; Lyons, LR; Deng, Y; Sheng, C; Bristow, WA; Donovan, EF; Angelopoulos, V; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 129 巻 ( 8 ) 2024年8月

Magnetic Storm-Time Red Aurora as Seen From Hokkaido, Japan on 1 December 2023 Associated With High-Density Solar Wind

Kataoka, R; Miyoshi, Y; Shiokawa, K; Nishitani, N; Keika, K; Amano, T; Seki, K

GEOPHYSICAL RESEARCH LETTERS 51 巻 ( 12 ) 2024年6月

Thermospheric Wind Response to March 2023 Storm: Largest Wind Ever Observed With a Fabry-Perot Interferometer in Tromsø, Norway Since 2009

Oyama, S; Vanhamäki, H; Cai, L; Shinbori, A; Hosokawa, K; Sakanoi, T; Shiokawa, K; Aikio, A; Virtanen, II; Ogawa, Y; Miyoshi, Y; Kurita, S; Nishitani, N

SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS 22 巻 ( 3 ) 2024年3月

Space weather with an arc's ∼2 h trip across the nightside polar cap

Lyons, LR; Nishimura, Y; Liu, J; Yadav, S; Zou, Y; Bristow, WA; Donovan, E; Nishitani, N

FRONTIERS IN ASTRONOMY AND SPACE SCIENCES 10 巻 2024年1月

New aspects of the upper atmospheric disturbances caused by the explosive eruption of the 2022 Hunga Tonga-Hunga Ha'apai volcano

Shinbori, A; Otsuka, Y; Sori, T; Nishioka, M; Septi, P; Tsuda, T; Nishitani, N; Kumamoto, A; Tsuchiya, F; Matsuda, S; Kasahara, Y; Matsuoka, A; Nakamura, S; Miyoshi, Y; Shinohara, I

EARTH PLANETS AND SPACE 75 巻 ( 1 ) 2023年11月

Nightside High-Latitude Phase and Amplitude Scintillation During a Substorm Using 1-Second Scintillation Indices

Nishimura, Y; Kelly, T; Jayachandran, PT; Mrak, S; Semeter, JL; Donovan, EF; Angelopoulos, V; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 128 巻 ( 8 ) 2023年8月

IMF Dependence of Midnight Bifurcation in the Thermospheric Wind at an Auroral Latitude Based on Nine Winter Measurements in Tromso, Norway

Oyama, S; Hosokawa, K; Vanhamäki, H; Aikio, A; Sakanoi, T; Cai, L; Virtanen, II; Shiokawa, K; Nishitani, N; Shinbori, A; Ogawa, Y

GEOPHYSICAL RESEARCH LETTERS 50 巻 ( 14 ) 2023年7月

Geomagnetic activity dependence and dawn-dusk asymmetry of thermospheric winds from 9-year measurements with a Fabry-Perot interferometer in Tromso, Norway

Oyama, SI; Aikio, A; Sakanoi, T; Hosokawa, K; Vanhamäki, H; Cai, L; Virtanen, I; Pedersen, M; Shiokawa, K; Shinbori, A; Nishitani, N; Ogawa, Y

EARTH PLANETS AND SPACE 75 巻 ( 1 ) 2023年5月

Unsolved problems: Mesoscale polar cap flow channels' structure, propagation, and effects on space weather disturbances

Lyons, LR; Nishimura, Y; Liu, J; Zou, Y; Bristow, WA; Yadav, S; Donovan, E; Nishitani, N; Shiokawa, K; Hosokawa, K

FRONTIERS IN ASTRONOMY AND SPACE SCIENCES 10 巻 2023年4月

First Detection of Midlatitude Plasma Bubble by SuperDARN During a Geomagnetic Storm on May 27 and 28, 2017

Sori, T; Shinbori, A; Otsuka, Y; Nishioka, M; Perwitasari, S; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 128 巻 ( 4 ) 2023年4月

Special issue "20th anniversary issue: earth, planetary, and space science in the next decade"

Ogawa, Y; Nishitani, N; Furuya, M; Acocella, V; Hussmann, H

EARTH PLANETS AND SPACE 75 巻 ( 1 ) 2023年1月

A Statistical Study of Longitudinal Extent of Pc1 Pulsations Using Seven PWING Ground Stations at Subauroral Latitudes

Liu, J; Shiokawa, K; Oyama, SI; Otsuka, Y; Jun, CW; Nose, M; Nagatsuma, T; Sakaguchi, K; Kadokura, A; Ozaki, M; Connors, M; Baishev, D; Nishitani, N; Oinats, A; Kurkin, V; Raita, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 128 巻 ( 1 ) 2023年1月

Oscillations of the Ionosphere Caused by the 2022 Tonga Volcanic Eruption Observed With SuperDARN Radars

Zhang, JJ; Xu, JY; Wang, W; Wang, GJ; Ruohoniemi, JM; Shinbori, A; Nishitani, N; Wang, C; Deng, X; Lan, AL; Yan, JY

GEOPHYSICAL RESEARCH LETTERS 49 巻 ( 20 ) 2022年10月

Geospace Concussion: Global Reversal of Ionospheric Vertical Plasma Drift in Response to a Sudden Commencement

Shi, XL; Lin, D; Wang, WB; Baker, JBH; Weygand, JM; Hartinger, MD; Merkin, VG; Ruohoniemi, JM; Pham, K; Wu, HN; Angelopoulos, V; McWilliams, KA; Nishitani, N; Shepherd, SG

GEOPHYSICAL RESEARCH LETTERS 49 巻 ( 19 ) 2022年10月

Unified Theory of the Arc Auroras: Formation Mechanism of the Arc Auroras Conforming General Principles of Convection and FAC Generation

Tanaka, T; Watanabe, M; Ebihara, Y; Fujita, S; Nishitani, N; Kataoka, R

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 9 ) 2022年9月

Interpretation of the Theta Aurora Based on the Null-Separator Structure

Tanaka, T; Ebihara, Y; Watanabe, M; Fujita, S; Nishitani, N; Kataoka, R

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 8 ) 2022年8月

Electromagnetic conjugacy of ionospheric disturbances after the 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption as seen in GNSS-TEC and SuperDARN Hokkaido pair of radars observations

Shinbori, A; Otsuka, Y; Sori, T; Nishioka, M; Perwitasari, S; Tsuda, T; Nishitani, N

EARTH PLANETS AND SPACE 74 巻 ( 1 ) 2022年7月

Interaction Between Proton Aurora and Stable Auroral Red Arcs Unveiled by Citizen Scientist Photographs

Nishimura, Y; Bruus, E; Karvinen, E; Martinis, CR; Dyer, A; Kangas, L; Rikala, HK; Donovan, EF; Nishitani, N; Ruohoniemi, JM

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 7 ) 2022年7月

On the Noise Estimation in Super Dual Auroral Radar Network Data

Ponomarenko, PV; Bland, EC; McWilliams, KA; Nishitani, N

RADIO SCIENCE 57 巻 ( 6 ) 2022年6月

Small-Scale Irregularities Within Polarization Jet/SAID During Geomagnetic Activity

Sinevich, AA; Chernyshov, AA; Chugunin, DV; Oinats, AV; Clausen, LBN; Miloch, WJ; Nishitani, N; Mogilevsky, MM

GEOPHYSICAL RESEARCH LETTERS 49 巻 ( 8 ) 2022年4月

Statistical Study of Seasonal and Solar Activity Dependence of Nighttime MSTIDs Occurrence Using the SuperDARN Hokkaido Pair of Radars

Hazeyama, W; Nishitani, N; Hori, T; Nakamura, T; Perwitasari, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 4 ) 2022年4月

Multi-Scale Density Structures in the Plasmaspheric Plume During a Geomagnetic Storm

Nishimura, Y; Goldstein, J; Martinis, C; Ma, Q; Li, W; Zhang, SR; Coster, AJ; Mrak, S; Semeter, JL; Nishitani, N; Ruohoniemi, JM; Shepherd, SG

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 3 ) 2022年3月

Statistical Characteristics of Mid-Latitude Ionospheric Irregularities at Geomagnetic Quiet Time: Observations From the Jiamusi and Hokkaido East SuperDARN HF Radars

Wang, W; Zhang, JJ; Wang, C; Nishitani, N; Yan, JY; Lan, AL; Deng, X; Qiu, HB

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 1 ) 2022年1月

Roles of the M-I Coupling and Plasma Sheet Dissipation on the Growth-Phase Thinning and Subsequent Transition to the Onset

Tanaka, T; Ebihara, Y; Watanabe, M; Den, M; Fujita, S; Kikuchi, T; Hashimoto, KK; Nishitani, N; Kataoka, R

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 12 ) 2021年12月

The Role of Flare-Driven Ionospheric Electron Density Changes on the Doppler Flash Observed by SuperDARN HF Radars

Chakraborty, S; Qian, L; Ruohoniemi, JM; Baker, JBH; McInerney, JM; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 8 ) 2021年8月

History of Japanese SuperDARN: Initiation of SENSU Syowa radars and progress of Japanese radar project

Sato, N; Ogawa, T; Yamagishi, H; Yukimatu, AS; Nishitani, N; Kikuchi, T; Nozaki, K; Igarashi, K; Nagatsuma, T

POLAR SCIENCE 28 巻 2021年6月

Development of remote HF wave receiver in the backlobe direction of the SuperDARN Hokkaido East radar: Initial observations

Nishitani, N; Hamaguchi, Y; Hori, T

POLAR SCIENCE 28 巻 2021年6月

Editorial: Special issue: "SuperDARN/Studies of Geospace Dynamics - Today and Future"

Yukimatu, AS; Grocott, A; Thomas, EG; Nagatsuma, T; Nishitani, N; Hosokawa, K; Watanabe, M

POLAR SCIENCE 28 巻 2021年6月

Evolution of Mid-latitude Density Irregularities and Scintillation in North America During the 7-8 September 2017 Storm

Nishimura, Y; Mrak, S; Semeter, JL; Coster, AJ; Jayachandran, PT; Groves, KM; Knudsen, DJ; Nishitani, N; Ruohoniemi, JM

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 6 ) 2021年6月

Cusp Dynamics and Polar Cap Patch Formation Associated With a Small IMF Southward Turning

Nishimura, Y; Sadler, FB; Varney, RH; Gilles, R; Zhang, SR; Coster, AJ; Nishitani, N; Otto, A

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 5 ) 2021年5月

Source Region and Propagation of Dayside Large-Scale Traveling Ionospheric Disturbances

Nishimura, Y; Zhang, SR; Lyons, LR; Deng, Y; Coster, AJ; Moen, JI; Clausen, LB; Bristow, WA; Nishitani, N

GEOPHYSICAL RESEARCH LETTERS 47 巻 ( 19 ) 2020年10月

Dayside Polar Cap Density Enhancements Formed During Substorms

Goodwin, LV; Nishimura, Y; Coster, AJ; Zhang, S; Nishitani, N; Ruohoniemi, JM; Anderson, BJ; Zhang, QH

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 125 巻 ( 10 ) 2020年10月

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

Martinez-Calderon, C; Nemec, F; Katoh, Y; Shiokawa, K; Kletzing, C; Hospodarsky, G; Santolik, O; Kasahara, Y; Matsuda, S; Kumamoto, A; Tsuchiya, F; Matsuoka, A; Shoji, M; Teramoto, M; Kurita, S; Miyoshi, Y; Ozaki, M; Nishitani, N; Oinats, AV; Kurkin, VI

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 125 巻 ( 9 ) 2020年9月

Dynamics of Auroral Precipitation Boundaries Associated With STEVE and SAID

Nishimura, Y; Donovan, EF; Angelopoulos, V; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 125 巻 ( 8 ) 2020年8月

Magnetospheric Conditions for STEVE and SAID: Particle Injection, Substorm Surge, and Field-Aligned Currents

Nishimura, Y; Yang, J; Weygand, JM; Wang, W; Kosar, B; Donovan, EF; Angelopoulos, V; Paxton, LJ; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 125 巻 ( 8 ) 2020年8月

On the Origin of Far-Aspect Angle Irregularity Regions Seen by HF Radars at 100-km Altitude

St-Maurice, JP; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 125 巻 ( 6 ) 2020年6月

A framework for estimating spherical vector fields using localized basis functions and its application to SuperDARN data processing

Nakano, S; Hori, T; Seki, K; Nishitani, N

EARTH PLANETS AND SPACE 72 巻 ( 1 ) 2020年4月

Comparison of SuperDARN peak electron density estimates based on elevation angle measurements to ionosonde and incoherent scatter radar measurements

Koustov, AV; Ullrich, S; Ponomarenko, PV; Gillies, RG; Themens, DR; Nishitani, N

EARTH PLANETS AND SPACE 72 巻 ( 1 ) 2020年3月

Unprecedented Hemispheric Asymmetries During a Surprise Ionospheric Storm: A Game of Drivers

Astafyeva, E; Bagiya, MS; Förster, M; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 125 巻 ( 3 ) 2020年3月

First Observation of Ionospheric Convection From the Jiamusi HF Radar During a Strong Geomagnetic Storm

Zhang, JJ; Wang, W; Wang, C; Lan, AL; Yan, JY; Xiang, D; Zhang, QH; Ruohoniemi, JM; Kunduri, BSR; Nishitani, N; Shi, X; Qiu, HB

EARTH AND SPACE SCIENCE 7 巻 ( 1 ) 2020年1月

Sluggishness of the Ionosphere: Characteristic time-lag in Response to Solar Flares

Chakraborty, S; Ruohoniemi, JM; Baker, JBH; Fiori, RAD; Zawdie, KA; Bailey, S; Nishitani, N; Drob, D

2020 XXXIIIRD GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM OF THE INTERNATIONAL UNION OF RADIO SCIENCE 2020年

Method for Estimating Neutral Wind Azimuth using 2D TID Propagation Parameters

Tolstikov, MV; Oinats, AV; Medvedeva, IV; Nishitani, N

2020 XXXIIIRD GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM OF THE INTERNATIONAL UNION OF RADIO SCIENCE 2020年

Occurrence of F region echoes for the polar cap SuperDARN radars

Koustov, AV; Ullrich, S; Ponomarenko, PV; Nishitani, N; Marcucci, FM; Bristow, WA

EARTH PLANETS AND SPACE 71 巻 ( 1 ) 2019年10月

Special issue "Recent Advances in MST and EISCAT/Ionospheric Studies - Special Issue of the Joint MST15 and EISCAT18 Meetings, May 2017" PREFACE

Yamamoto, M; Hocking, WK; Nozawa, S; Vierinen, J; Liu, HX; Nishitani, N

EARTH PLANETS AND SPACE 71 巻 ( 1 ) 2019年9月

A Study of SuperDARN Response to Co-occurring Space Weather Phenomena

Chakraborty, S; Baker, JBH; Ruohoniemi, JM; Kunduri, B; Nishitani, N; Shepherd, SG

SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS 17 巻 ( 9 ) 頁： 1351 - 1363 2019年9月

Review of the accomplishments of mid-latitude Super Dual Auroral Radar Network (SuperDARN) HF radars (vol 6 , pg 27, 2019)

Nishitani, N; Ruohoniemi, JM; Lester, M; Baker, JBH; Koustov, AV; Shepherd, SG; Chisham, G; Hori, T; Thomas, EG; Makarevich, RA; Marchaudon, A; Ponomarenko, P; Wild, JA; Milan, SE; Bristow, WA; Devlin, J; Miller, E; Greenwald, RA; Ogawa, T; Kikuchi, T

PROGRESS IN EARTH AND PLANETARY SCIENCE 6 巻 2019年7月

Global Diagnostics of Ionospheric Absorption During X-Ray Solar Flares Based on 8-to 20-MHz Noise Measured by Over-the-Horizon Radars

Berngardt, OI; Ruohoniemi, JM; St-Maurice, JP; Marchaudon, A; Kosch, MJ; Yukimatu, AS; Nishitani, N; Shepherd, SG; Marcucci, MF; Hu, H; Nagatsuma, T; Lester, M

SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS 17 巻 ( 6 ) 頁： 907 - 924 2019年6月

Response of the Ionosphere-Plasmasphere Coupling to the September 2017 Storm:What Erodes the Plasmasphere so Severley?

Obana, Y; Maruyama, N; Shinbori, A; Hashimoto, KK; Fedrizzi, M; Nosé, M; Otsuka, Y; Nishitani, N; Hori, T; Kumamoto, A; Tsuchiya, F; Matsuda, S; Matsuoka, A; Kasahara, Y; Yoshikawa, A; Miyoshi, Y; Shinohara, I

SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS 17 巻 ( 6 ) 頁： 861 - 876 2019年6月

Local time extent of magnetopause reconnection using space-ground coordination

Zou, Y; Walsh, BM; Nishimura, Y; Angelopoulos, V; Ruohoniemi, JM; McWilliams, KA; Nishitani, N

ANNALES GEOPHYSICAE 37 巻 ( 2 ) 頁： 215 - 234 2019年4月

Review of the accomplishments of mid-latitude Super Dual Auroral Radar Network (SuperDARN) HF radars

PROGRESS IN EARTH AND PLANETARY SCIENCE 6 巻 2019年3月

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

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

NATURE COMMUNICATIONS 10 巻 2019年1月

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, RC; Tanaka, YM; 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) 頁： . 2019年

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

Beletskii, AB; Rakhmatulin, RA; Syrenova, TY; Vasilev, RV; Mikhalev, AV; Pashinin, AY; Shiokawa, K; Nishitani, N

SOLAR-TERRESTRIAL PHYSICS 5 巻 ( 2 ) 頁： 39 - 44 2019年

Relation of Traveling Ionospheric Disturbances Characteristics with Planetary Waves in the Middle Atmosphere

Tolstikov, MV; Oinats, AV; Medvedeva, IV; Medvedev, AV; Ratovsky, KG; Nishitani, N

2019 PHOTONICS & ELECTROMAGNETICS RESEARCH SYMPOSIUM - SPRING (PIERS-SPRING) 頁： 2176 - 2182 2019年

Microscopic Observations of Pulsating Aurora Associated With Chorus Element Structures: Coordinated Arase Satellite-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, RC; Tanaka, YM; Nosé, 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 45 巻 ( 22 ) 頁： 12125 - 12134 2018年11月

Driving of strong nightside reconnection and geomagnetic activity by polar cap flows: Application to CME shocks and possibly other situations

Lyons, LR; Gallardo-Lacourt, B; Zou, Y; Nishimura, Y; Anderson, P; Angelopoulos, V; Donovan, EF; Ruohoniemi, JM; Mitchell, E; Paxton, LJ; Nishitani, N

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 177 巻頁： 73 - 83 2018年10月

Substorm-Associated Ionospheric Flow Fluctuations During the 27 March 2017 Magnetic Storm: SuperDARN-Arase Conjunction

Hori, T; Nishitani, N; Shepherd, SG; Ruohoniemi, JM; Connors, M; Teramoto, M; Nakano, S; Seki, K; Takahashi, N; Kasahara, S; Yokota, S; Mitani, T; Takashima, T; Higashio, N; Matsuoka, A; Asamura, K; Kazama, Y; Wang, SY; Tam, SWY; Chang, TF; Wang, BJ; Miyoshi, Y; Shinohara, I

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 18 ) 頁： 9441 - 9449 2018年9月

A New Empirical Model of the Subauroral Polarization Stream

Kunduri, BSR; Baker, JBH; Ruohoniemi, JM; Nishitani, N; Oksavik, K; Erickson, PJ; Coster, AJ; Shepherd, SG; Bristow, WA; Miller, ES

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 123 巻 ( 9 ) 頁： 7342 - 7357 2018年9月

Temporal and Spatial Variations of Storm Time Midlatitude Ionospheric Trough Based on Global GNSS-TEC and Arase Satellite Observations

Shinbori, A; Otsuka, Y; Tsugawa, T; Nishioka, M; Kumamoto, A; Tsuchiya, F; Matsuda, S; Kasahara, Y; Matsuoka, A; Ruohoniemi, JM; Shepherd, SG; Nishitani, N

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 15 ) 頁： 7362 - 7370 2018年8月

Attenuation of decameter wavelength sky noise during x-ray solar flares in 2013-2017 based on the observations of midlatitude HF radars

Berngardt, OI; Ruohoniemi, JM; Nishitani, N; Shepherd, SG; Bristow, WA; Miller, ES

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 173 巻頁： 1 - 13 2018年8月

The ERG Science Center

Miyoshi, Y; Hori, T; Shoji, M; Teramoto, M; Chang, TF; Segawa, T; Umemura, N; Matsuda, S; Kurita, S; Keika, K; Miyashita, Y; Seki, K; Tanaka, Y; Nishitani, N; Kasahara, S; Yokota, S; Matsuoka, A; Kasahara, Y; Asamura, K; Takashima, T; Shinohara, I

EARTH PLANETS AND SPACE 70 巻 2018年6月

Characterization of Short-Wave Fadeout Seen in Daytime SuperDARN Ground Scatter Observations

Chakraborty, S; Ruohoniemi, JM; Baker, JBH; Nishitani, N

RADIO SCIENCE 53 巻 ( 4 ) 頁： 472 - 484 2018年4月

Spreading Speed of Magnetopause Reconnection X-Lines Using Ground-Satellite Coordination

Zou, Y; Walsh, BM; Nishimura, Y; Angelopoulos, V; Ruohoniemi, JM; McWilliams, KA; Nishitani, N

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 1 ) 頁： 80 - 89 2018年1月

Influence of Auroral Streamers on Rapid Evolution of Ionospheric SAPS Flows

Gallardo-Lacourt, B; Nishimura, Y; Lyons, LR; Mishin, EV; Ruohoniemi, JM; Donovan, EF; Angelopoulos, V; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 12 ) 頁： 12406 - 12420 2017年12月

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, K; Katoh, Y; Hamaguchi, Y; Yamamoto, Y; Adachi, T; Ozaki, M; Oyama, SI; Nosé, M; Nagatsuma, T; Tanaka, Y; Otsuka, Y; Miyoshi, Y; Kataoka, R; Takagi, Y; Takeshita, Y; Shinbori, A; Kurita, S; Hori, T; Nishitani, N; Shinohara, I; Tsuchiya, F; Obana, Y; Suzuki, S; Takahashi, N; Seki, K; Kadokura, A; Hosokawa, K; Ogawa, Y; Connors, M; Ruohoniemi, JM; Engebretson, M; Turunen, E; Ulich, T; Manninen, J; Raita, T; Kero, A; Oksanen, A; Back, M; Kauristie, K; Mattanen, J; Baishev, D; Kurkin, V; Oinats, A; Pashinin, A; Vasilyev, R; Rakhmatulin, R; Bristow, W; Karjala, M

EARTH PLANETS AND SPACE 69 巻 2017年11月

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

Watanabe, T; Iyemori, T; Shiokawa, K; Zhang, J; Kanekal, S; Nishitani, N

EARTH PLANETS AND SPACE 69 巻 2017年11月

SC-Associated Electric Field Variations in the Magnetosphere and Ionospheric Convective Flows

Kim, SI; Kim, KH; Kwon, HJ; Jin, H; Lee, E; Jee, G; Nishitani, N; Hori, T; Lester, M; Wygant, JR

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 11 ) 頁： 11044 - 11057 2017年11月

Propagation and evolution of electric fields associated with solar wind pressure pulses based on spacecraft and ground-based observations

Takahashi, N; Kasaba, Y; Nishimura, Y; Shinbori, A; Kikuchi, T; Hori, T; Ebihara, Y; Nishitani, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 122 巻 ( 8 ) 頁： 8446 - 8461 2017年8月

First imaging and identification of a noctilucent cloud from multiple sites in Hokkaido (43.2-44.4 N), Japan 査読有り

Hidehiko Suzuki, Kazuyo Sakanoi, Nozomu Nishitani, Tadahiko Ogawa, Mitsumu K. Ejiri, Minoru Kubota, Takenori Kinoshita, Yasuhiro Murayama and Yasushi Fujiyoshi

Earth, Planets and Space 68:182 巻 2016年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

Simultaneous imaging observations of a noctilucent cloud (NLC) from five sites in Hokkaido, Japan (43.17-45.36 N), were successfully carried out using digital cameras in the early hours of the morning (around 02:00 LST) on June 21, 2015. This is the first NLC event that has been captured from multiple sites in Japan. The simultaneous images obtained from multiple sites made it possible to calculate the exact altitude (=83.9 +- 0.1 km) and spatial distribution (47.5-50.0 N and 143.0-147.5 E) of the NLC by triangulation and image correlation methods. Based on a comparison of atmospheric parameters of the upper mesosphere provided by satellites and a middle-frequency (MF) radar in northern Hokkaido (Wakkanai) with the cloud distribution obtained from the Aeronomy of Ice in the Mesosphere satellite, this particular event is considered to be the result of southward advection of the NLC from a higher-latitude (i.e., colder) region. Anomalies in the upper mesospheric temperature of the northern hemispheric summer in 2015 were examined using AURA satellite data, because this is the first NLC event that has been identified in Japan. However, no remarkable temperature variations relative to other years were found in upper mesosphere. Based on a comparison between the NLC period and the record of sky conditions archived by the Japan Meteorological Agency, a high percentage of cloud (especially low-level) cover during the summer in Hokkaido cannot be ruled out as a possible reason why the NLC had not previously been sighted in Hokkaido.

DOI： 10.1186/s40623-016-0562-6

Application of ground scatter returns for calibration of HF interferometry data 査読有り

Ponomarenko, P., N. Nishitani, A.V. Oinats, T. Tsuya and J.-P. St.-Maurice

Earth Planets Space 67 巻 ( 138 ) 2015年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

Information on the vertical angle of arrival (elevation) is crucial in determining propagation modes of high-frequency (HF, 3-30 MHz) radio waves travelling through the ionosphere. The most advanced network of ionospheric HF radars, SuperDARN (Super Dual Auroral Radar Network), relies on interferometry to measure elevation, but this information is rarely used due to intrinsic difficulties with phase calibration as well as with the physical interpretation of the measured elevation patterns. In this work, we propose an empirical method of calibration for SuperDARN interferometry. The method utilises a well-defined dependence of elevation on range of ground scatter returns. "Fine tuning" of the phase is achieved based on a detailed analysis of phase fluctuation effects at very low elevation angles. The proposed technique has been successfully applied to data from the mid-latitude Hokkaido East SuperDARN radar. It can also be used at any other installation that utilises HF interferometry.

DOI： doi: 10.1186/s40623-015-0310-3

Occurrence characteristics and lowest speed limit of Sub-Auroral Polarization Stream (SAPS) observed by the SuperDARN Hokkaido East radar 査読有り

Nagano, H., N. Nishitani, and T. Hori

Earth Planets Space 67 巻 ( 126 ) 2015年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

We investigate the characteristics of the subauroral polarization stream (SAPS), with focus on the relationship between geomagnetic parameters and occurrence characteristics of SAPS. This study's observations were made using the Super Dual Auroral Radar Network (SuperDARN) Hokkaido East radar, which can observe the Far East region of Russia and has been in operation since 2006. In particular, we identify the lowest limit of SAPS speed, which has not been discussed in previous literature, in order to examine the lowest threshold of electric field able to generate SAPS as a result of magnetosphere-ionosphere (M-I) coupling. In order to conduct a comprehensive investigation of SAPS occurrence characteristics, we analyzed events with wider ranges of velocity and magnetic latitude (MLAT) than those in previous studies. As a result of quantitative estimation, we found two categories of westward flows that were reasonably separated using a speed threshold of 150-200 m/s. For the faster flows above the speed threshold, there is a clear correlation between MLAT and SYM-H geomagnetic index, whereas for the slower flows, there is no such correlation. The faster flows are considered to be SAPS, whereas the slower flows are probably associated with mid-latitude F-region ionospheric irregularities not directly related to storms or substorms. This slowest limit of SAPS gives us a minimum electric field of 7.5-10 mV/m that generates SAPS. However, this field strength is not strong enough to cause frictional heating, which is generally considered to be a crucial mechanism for generating SAPS. This result suggests that frictional heating is not always necessary to generate SAPS.

DOI： 10.1186/s40623-015-0299-7

Statistical study of medium-scale traveling ionospheric disturbances using SuperDARN Hokkaido ground backscatter data for 2011 査読有り

Oinats, A.V., V.I. Kurkin, and N. Nishitani

Earth Planets Space 67 巻 ( 22 ) 2015年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

We describe an automated technique to determine parameters of traveling ionospheric disturbances (TIDs) using the Super Dual Auroral Radar Network (SuperDARN) high frequency (HF) radar data. The technique is based on the analysis of minimum ground backscatter range variations corresponding to different radar beams. Using this technique, we processed the SuperDARN Hokkaido radar data for 2011 and revealed statistical distributions of medium-scale TID (MSTID) azimuth and apparent horizontal velocity. We found four peaks with a distinct diurnal and seasonal dependence in the MSTID azimuth occurrence rate distributions. Northeast MSTID azimuths (20° to 50°) are typical of the summer and equinox morning hours; southeast azimuths (100° to 140°) prevail in the winter daytime; southwest azimuths (190° to 220°) are typical mostly in the summer and equinox nighttime and in the equinox evening; northwest azimuths (280° to 320°) are typical of the summer daytime and evening. The apparent horizontal velocities are generally within the 100 to 160 m/s range. The obtained results agree well with earlier studies by other researchers. However, there are also certain differences. The summer daytime northwestward MSTIDs are not indicated in the earlier studies. The nighttime horizontal velocities are 1.5 to 2 times higher than those in the daytime. Furthermore, winter velocity values are about 1.5 times higher than those in other seasons. These differences might be associated with the peculiarities of the data recorded by different facilities, or the features of the processing techniques, and require further investigation for their interpretation.

DOI： 10.1186/s40623-015-0192-4

Pi2 pulsation simultaneously observed in the E and F region ionosphere with the SuperDARN Hokkaido radar 査読有り

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

J. Geophys. Res. 119 巻頁： 3444-3462 2014年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 (8 s) 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 110 s 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 ~8.0mV/m
in the F region and ~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 from6 nT (MSR) to 10 nT (STC). At the dominant frequency of 8.8 mHz, the coherences between H and EEW were high (>0.9), the cross phases of EEW relative to H were 56°and 45°, and the amplitude ratios were 2.7 × 105m/s and 8.4 × 105 m/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 Alfvén waves must be taken in account.

DOI： 10.1002/2012JA018585

Hokkaido HF radar signatures of periodically reoccurring nighttime MSTIDs detected at short ranges 査読有り

Koustov, A.V., K. N. Yakymenko, N. Nishitani, and P. V. Ponomarenko

J. Geophys. Res. 119 巻頁： 1200-1218 2014年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

The Super Dual Auroral Radar Network Hokkaido HF radar often detects periodically reoccurring E region echoing regions propagating toward or away from it. In this work, we consider 117 of such events identified for 2008-2012. These are shown to occur at nighttime, preferentially during summer, although significant number for events was found for winter. Statistics for the local time of occurrence, magnitude of the speed and polarity of progressions, and temporal and spatial periodicities are presented. We show that the power of echoes is linearly related to their Doppler velocity which makes it possible to identify the events on both power and Doppler velocity plots. Other peculiar characteristics of echoes are discussed. The onset of
events is associated with gravity waves propagation through the radar field of view.

DOI： 10.1002/2013JA019422

Study of mid-latitude ionospheric convection during quiet and disturbed periods using the SuperDARN Hokkaido radar 査読有り

Zou, Y., and N. Nishitani

Advances in Space Research 54 巻頁： 473-480 2014年1月

Northward-propagating nighttime medium-scale traveling ionospheric disturbances observed with the SuperDARN Hokkaido HF radar and GEONET 査読有り

Ichihara, A., N. Nishitani, T. Ogawa, and T. Tsugawa

Advances in Polar Science 頁： in press 2013年

Study of ionospheric disturbances during solar flare events with the SuperDARN Hokkaido Radar 査読有り

Watanabe, D., and N. Nishitani

Adv. Polar Sci. 24 巻頁： 12-18 2013年

Propagation of large amplitude ionospheric disturbances with velocity dispersion observed by the SuperDARN Hokkaido radar after the 2011 off the Pacific coast of Tohoku Earthquake 査読有り

Nishitani, N., T. Ogawa, Y. Otsuka, K. Hosokawa, and T. Hori

Earth Planets Space 63 巻頁： 891-896 2011年9月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Ionospheric responses to the 2011 off the Pacific coast of Tohoku Earthquake are studied using the SuperDARN Hokkaido radar, which is located at (43.5^o N, 143.6^o E) and which monitors the ionosphere over a wide horizontal area. The radar observed an oscillation of the vertical motion of the ionosphere with a period of about 1 to 2 min. The disturbance propagated northward, away from the epicenter with the velocity of about 6.2, 4.5, 3.9 and 3.5 km/s. The latter three values are basically consistent with the propagation of the Earth's surface waves reported in several previous studies. The propagation velocities decreased with time, which has not been reported in previous studies for this propagation velocity range. The peak-to-peak amplitudes of Doppler velocities of ground/sea scatter echoes observed by the radar were up to 200 m/s, which is considerably larger than previously-reported values using HF Doppler measurements, although they are not extremely large for this historical earthquake (M = 9.0). This is the first time that ionospheric data have been obtained with high temporal (8 s) and spatial (22.5 km) resolutions following a giant earthquake, which enables us to discuss the detailed characteristics of the propagation of coseismic ionospheric disturbances.

DOI： doi:10.5047/eps.2011.07.003

Large-Scale traveling ionospheric disturbance observed by SuperDARN Hokkaido HF radar and GPS networks on 15 December 2006 査読有り

Hayashi, H., N. Nishitani, T. Ogawa, Y. Otsuka, T. Tsugawa, K. Hosokawa, and A. Saito

J. Geophys. Res. 115 巻 ( A06309 ) 頁： doi:10.1029/2009JA014297 2010年

*Medium-scale traveling ionospheric disturbancesobserved with the SuperDARN Hokkaido radar, all-sky imager and GPS network, and their relation to concurrent sporadic-E irregularities 査読有り

Ogawa, T., N. Nishitani, Y. Otsuka, K. Shiokawa, T. Tsugawa,and K. Hosokawa

J. Geophys. Res. 114 巻頁： A03316, doi:10.1029/2008JA013893 2009年

記述言語：英語掲載種別：研究論文（学術雑誌）

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
55–25N. 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.

Joint observations of a traveling ionospheric disturbance with the Paratunka OMTI camera and the Hokkaido HF radar 査読有り

Koustov, A.V., N. Nishitani, K. Shiokawa, S. Suzuki, and B.M. Shevtsov

Ann. Geophys. 27 巻頁： 2399-2406 2009年

Subauroral polarization streams: observations with the Hokkaido and King SalmonSuperDARN radars and modeling 査読有り

Koustov, A.V., N. Nishitani, Y. Ebihara, T. Kikuchi, M.R. Hairston, and D. Andre

Ann. Geophys. 26 巻頁： 3317-3327 2008年

*Dynamical property of storm-time subauroral rapid flows as amanifestation of complex structures of the plasma pressure in the inner magnetosphere 査読有り

Ebihara, Y., N. Nishitani, T. Kikuchi, T. Ogawa, K. Hosokawa, M. -C. Fok and M. F. Thomsen

J. Geophys. Res. 114 巻頁： A01306, doi:10.1029/2008JA013614 2008年

記述言語：英語掲載種別：研究論文（学術雑誌）

During the intense magnetic storm of 15 December 2006, the midlatitude Super Dual Auroral Radar Network (SuperDARN) Hokkaido radar observed a dynamical character of rapid, westward flows at 50–56 magnetic latitude. The simulation that couples the inner magnetosphere and the subauroral ionosphere was performed using a realistic boundary condition of the hot ion distribution determined from four Los Alamos National Laboratory satellites at 6.6 R E . The following results are obtained using the simulation: (1) In general, morphology of the azimuthal component of the simulated ionospheric plasma flow is consistent with that known as the subauroral polarization stream (SAPS), (2) an increase in the hot ion density in the plasma sheet results in the temporal reduction and subsequent intensification of the rapid flow at certain subauroral latitudes with a delay of ∼40 min, and (3) influence of the plasma sheet temperature on the rapid flow is not evident. The simulated line-of-sight velocity is compared with that obtained by the SuperDARN Hokkaido radar. Agreement between them is found in terms of the temporal and spatial variations of the rapid flows as well as the flow velocity. It is suggested that the dynamical character of the subauroral plasma flow is a direct manifestation of the plasma pressure distribution in the inner magnetosphere (the ring current) especially during the magnetic storm.

Two-dimensional observations of overshielding during a magnetic storm by the SuperDARN Hokkaido radar 査読有り

Ebihara, Y., N. Nishitani, T. Kikuchi, T. Ogawa, K. Hosokawa, and M. -C. Fok

Journal of Geophysical Research 113 巻 ( A01213 ) 頁： doi:10.1029/2007JA012641 2008年

記述言語：英語掲載種別：研究論文（学術雑誌）

Two-dimensional observations of ionospheric plasma flows possibly caused by overshielding are reported for the first time. The observations were made by the mid-latitude SuperDARN Hokkaido radar in Japan during a major magnetic storm on December 15, 2006. The magnetosphere was exposed continuously to a southward interplanetary magnetic field (IMF) for several hours during the main phase of the storm. Immediately following the subsequent northward turning of the IMF, an anti-sunward plasma flow was observed for about 14 min in the pre-dusk sector at magnetic latitudes of 50-60°, reaching a maximum line-of-sight speed of 70-80 m/s. These features are consistent with a simulation of coupling between the ring current and the ionosphere associated with an overshielding condition. Within 1 h of the first observation, a similar anti-sunward flow was observed during a period of southward-oriented IMF. However, the simulation cannot account for the anti-sunward flow in this case. It is suggested that the shielding/overshielding condition is not simply caused by the northward turning of IMF. This second overshielding-like condition is attributable to a sudden contraction of the polar cap associated with the substorm, or to a sudden strengthening of the inertial current converted from the abrupt injection of magnetospheric ions. However, none of both fully accounts for the observations.

Dynamic variations of a convection flow reversal in the subauroral post-midnight sector as seen by the SuperDARN Hokkaido HF radar 査読有り

Ryuho Kataoka, Nozomu Nishitani, Yusuke Ebihara, Keisuke Hosokawa, Tadahiko Ogawa, Takashi Kikuchi, and Yoshizumi Miyoshi

Geophysical Research Letters 32 巻頁： L21105, doi:10.1029/2007GL031552 2007年

記述言語：英語掲載種別：研究論文（学術雑誌）

SuperDARN Hokkaido HF radar, capable of measuring the subauroral ionospheric plasma convection especially during storms, has been in continuous operation since the beginning of December 2006. We report the first two-dimensional observation of a dynamic variation of convection flow reversal in subauroral postmidnight sector during the storm main phase on 29 January 2007. The flow reversal region is extended over 20° in longitude and 5° in latitude, lasting for about 10-15 min, and the maximum flow speed is about 0.5-1.0 km/s. The flow reversal structure is reasonably reproduced by the ring current simulation coupled with the ionosphere, suggesting that it is produced by the region 2 field-aligned current associated with the ring current enhancement during the storm main phase. The dynamic variation of the flow reversal structure is interpreted as a transient eastward extension of the elongated dusk convection cell to the postmidnight and equatorward of the dawn cell, associated with the variation of the ring current whose structure is controlled by the interplanetary magnetic field and solar wind dynamic pressure. It is suggested that the ring current variation is highly coupled with the interplanetary parameters and is much more complicated than ever thought.

Model calculations of possible ionospheric backscatter echo area for a mid-latitude HF radar 査読有り

Nishitani, N., and T. Ogawa

Adv. Polar Upper Atmos. Res. 19 巻頁： 55-62 2005年8月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

HF ray path calculation is performed in order to identify possible
ionospheric backscatter echo area for an HF radar at mid-latitude. The calculation is
made on the basis of the R.M. Jones and J. J. Stephenson (U.S. Dept. of Commerce,
OT Rep. 75-76, 1975) HF ray path tracing algorithm plus the IRI-2001 ionosphere
model. It is shown that depending on the local time and geomagnetic activity, the
possible ionospheric backscatter regions have different distributions. In any case the
backscatter region is large enough, indicating the capability of a planned HF radar in
Hokkaido (43.5 N, 143.6 E), Japan.

*Unusual ionospheric echoes with high velocity and very low spectral width observed by the SuperDARN radars in the polar cap during high geomagnetic activity 査読有り

Nishitani, N., M. Lester, S. E. Milan, T. Ogawa, N. Sato, H. Yamagishi, A. S. Yukimatu, and F. J. Rich

Journal of Geophysical Research 109 巻 ( A2 ) 頁： A02311, doi:10.1029/2003JA010048 2004年2月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

The spectral width of the ionospheric backscatter echoes obtained with the SuperDARN radars has been regarded as a useful tool for locating specific ionospheric regions such as the cusp. In this paper we report the presence of ionospheric echoes with high (> 450 m/s) Doppler velocity and very low (< 60 m/s) spectral width, observed by the CUTLASS and Syowa East and South SuperDARN radars. These echoes have the following characteristics. (1) They have a close correlation with geomagnetic activity such that as the Dst index decreases, the radars tend to observe ionospheric echoes with high Doppler velocity and very low spectral width more frequently. (2) Their existence does not depend on magnetic local time. (3) They are located preferably in the polar cap region, where anti-sunward convection prevails. (4) They sometimes exist over a wide range, so they are more likely to be F-region rather than E-region echoes. The occurrence of these echoes during active periods is associated with the suppression of the electric field turbulence. The present result appears consistent with the previous paper by Golovchanskaya et al. [2002], who showed the negative correlation between the electric field turbulence level and geomagnetic activity.

*Interhemispheric asymmetry of the high latitude ionospheric convection on May 11-12, 1999 査読有り

Nishitani, N., V. Papitashvili, T. Ogawa, N. Sato, H. Yamagishi, A.S. Yukimatu, and F.J. Rich

Journal of Geophysical Research 108 巻 ( A5 ) 頁： 1184, doi:10.1029/2002JA009680 2003年5月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Ionospheric convection over the southern polar cap on May 11-12, 1999 has been studied by using the Syowa East and South HF radar data and the DMSP ion driftmeter data, when the solar wind density was very low and geomagnetic activity was low. The overall convection pattern is consistent with the previous results by Ohtani et al. [2000]. However, the Syowa radars and the DMSP satellites observed very high (> 1500 m/s) westward plasma flows at dusk directed from the nightside toward the dayside only in the southern (dark) hemisphere. The high-speed flow was observed continuously across the fields of view of both radars from 1530 UT on May 11 to 0200 UT on May 12, when the solar wind density was close to minimum. Comparison with the DMSP particle and auroral image data shows that the westward flow regions were located in the middle of the auroral precipitation area. The strong asymmetry of the convection between the two hemispheres indicates the importance of the presence (absence) of solar illumination for the absence (presence) of the strong and localized ionospheric flows.

*A study of the dusk convection cell's response to an IMF southward turning 査読有り

Nishitani, N., T. Ogawa, N. Sato, H. Yamagishi, M. Pinnock, J.-P. Villain, G. Sofko, and O. Troshichev

Journal of Geophysical Research 107 巻 ( A3 ) 頁： 10.1029/2001JA900095 2002年3月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

One example of the response of ionospheric convection and the polar cap boundary to a sudden change in the IMF orientation has been studied when the IMF suddenly changed from northward (+6 nT) to strongly southward (-19 nT), at 1716 UT on September 5, 1995, The Bz component was fairly constant for about 2 hours before and about 25 min after the sudden IMF change. The convection flow changed almost simultaneously over a global extent. This initial change of the convection pattern can be characterized by a sudden formation of a large flow vortex in the afternoon sector. On the other hand, the response of the polar cap boundary (or its proxy) is more complicated. The radar and particle data indicate the immediate equatorward expansion of the precipitation regions in the noon and premidnight sectors. About 10 to 20 minutes after the initial change, there were changes observed in the dusk region, namely an equatorward expansion of the current reversal boundary in the dusk sector between 1740 and 1750 UT, and an equatorward expansion of the convection reversal boundary. The delayed responses were observed 18 to 8 minutes before a substorm onset was recorded at mid-latitude stations at 1756 UT. These observations indicate that there were two kinds of ionospheric responses to the southward turning of the IMF; the first response is the formation of the convection vortex and the equatorward shift of the polar cap boundary at noon and at 21 MLT, and the second response is the equatorward expansion of the convection reversal boundary in the dusk sector. We make the case that the first response is associated with the propagation of magnetosonic waves, and that the second response is consistent with the Cowley and Lockwood [1992] picture of the redistribution of the newly created open flux in the polar cap region.

A very large scale flow burst observed by the SuperDARN radars 査読有り

Nozomu Nishitani, Tadahiko Ogawa, Mike Pinnock, Mervyn Freeman, John Dudeney, Jean-Paul Villain, Kile B. Baker, Natsuo Sato, Hisao Yamagishi, and Haruhisa Matsumoto

Journal of Geophysical Research 104 巻 ( 10 ) 頁： 22469 1999年10月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

We examined the dynamics of the ionospheric plasma in the dayside sector by using the HF radar data at Iceland West and at Finland from 1100 to 1230 UT on September 5, 1995. During that period, the solar wind density was high and the IMF was strongly southward. The dayside magnetopause was highly compressed nearly to the geosynchronous orbit. The two radars simultaneously detected a poleward flow burst in the noon sector which, assuming uniformity of flow in the region of the data gap (1.5 h of MLT) between the two radars, showed a magnetic local time extent of 5 hours. This local time extent is 2 to 3 hours wider than previous results. The maximum poleward plasma velocity of the flow burst is about 750 m/s, and the latitudinal size of the flow burst region is about 100 to 200 km. This flow burst region initially expanded in longitude up to 5 hours, and then shifted poleward with a phase speed of 400 to 670 m/s. The flow burst has a duration of about 20 minutes. This large-scale poleward flow burst is likely to be due to large-scale reconnection occurring at the dayside magnetopause and subsequent convection as the magnetic field lines are transported across the polar cap.

Averaged Pattern of Ionospheric Echo Region and Convection : Initial Results From the Syowa Station HF radar

Proceedings of the NIPR Symposium on Upper Atmospheric Physics 10 巻頁： 42 1997年

Spatial and Temporal Characteristics of Giant Undulations

Geophysical Research Letters 21 巻 ( 24 ) 頁： 2673 1994年

Auroral activity and corresponding magnetic signatures at synchronous orbit

Journal of Geomagnetism and Geoelectricity 40 巻頁： 4 1988年

　前のページ - 次のページ　

<西谷 望>

論文 - 西谷 望

<西谷　望>

論文 - 西谷　望