研究者詳細 - JUN Chae-Woo

論文 - JUN Chae-Woo

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EMIC Wave Properties Associated With and Without Injections in The Inner Magnetosphere 査読有り

C.‐W. Jun, C. Yue, J. Bortnik, L. R. Lyons, Y. Nishimura, C. Kletzing

Journal of Geophysical Research: Space Physics 124 巻 ( 3 ) 頁： 2029 - 2045 2019年3月

A Statistical Study of EMIC Waves Associated With and Without Energetic Particle Injection From the Magnetotail 査読有り

C.‐W. Jun, C. Yue, J. Bortnik, L. R. Lyons, Y. Nishimura, C. Kletzing, J. Wygant, H. Spence

Journal of Geophysical Research: Space Physics 124 巻 ( 1 ) 頁： 433 - 450 2019年1月

Possible generation mechanisms for Pc1 pearl structures in the ionosphere based on 6 years of ground observations in Canada, Russia, and Japan 査読有り Open Access

Jun C.W., Shiokawa K., Connors M., Schofield I., Poddelsky I., Shevtsov B.

Journal of Geophysical Research: Space Physics 121 巻 ( 5 ) 頁： 4409 - 4424 2016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）出版者・発行元：Journal of Geophysical Research: Space Physics

We investigate pearl structures (amplitude modulations) of Pc1 pulsations simultaneously observed at Athabasca (ATH, 54.7°N, 246.7°E, L = 4.3) in Canada, Magadan (MGD, 60.1°N, 150.7°E, L = 2.6) in Russia, and Moshiri (MOS, 44.4°N, 142.3°E, L = 1.5) in Japan. From 6 years of ground observations, from 2008 to 2013, we selected 84 Pc1 events observed simultaneously at the longitudinally separated stations (ATH and MGD) and 370 events observed at the latitudinally separated stations (MGD and MOS), all with high coherence (>0.7) of Pc1 waveforms. We calculated the cross-correlation coefficient (similarity: r) for the Pc1 pearl structures and found that more than half of the events in both pairs had low similarity (r < 0.7), indicating that most Pc1 waves exhibit different pearl structures at different stations. We found that high-similarity Pc1 pearl structures (r > 0.7) at the longitudinally separated stations are concentrated from 6 to 15 UT when both stations are in the nighttime. The similarity of Pc1 pearl structures tends to show a negative correlation with the standard deviation of the polarization angle in both pairs. The observed repetition period of Pc1 pearl structures has a clear positive correlation with the repetition period estimated from Pc1 bandwidth by assuming beating of different frequencies. From these results, we suggest that ionospheric beating effect could be a dominant process for the generation of Pc1 pearl structures. Beating processes in the ionosphere with a spatially distributed ionospheric source can cause the different shapes of Pc1 pearl structures at different observation points during ionospheric duct propagation.

DOI： 10.1002/2015ja022123

In Situ Observations of the Influence of Nonlinear EMIC Waves on Relativistic Electrons in the Outer Radiation Belt Open Access

Jun C.W., Miyoshi Y., Hori T., Bortnik J., Lyons L., Kim K.H., Mitani T., Takashima T., Shinohara I., Higashio N., Matsuoka A., Yamamoto K., Teramoto M.

Geophysical Research Letters 52 巻 ( 9 ) 2025年5月

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

This study demonstrates the influence of electromagnetic ion cyclotron (EMIC) rising-tone emissions on relativistic electrons in the inner magnetosphere using data obtained from the Van Allen Probes and Arase satellites. We find that the intense EMIC rising-tone emissions occur during the increase in the solar wind pressures, creating favorable conditions for triggering nonlinear wave growth. The strong flux drop-out of relativistic electrons in the parallel directions of the magnetic field, with energies of 0.2–4 MeV, was associated with the wave activity. We calculated the nonlinear triggering conditions and the minimum resonant energy of relativistic electrons interaction with EMIC waves, based on our observations. We conclude that EMIC rising-tone emissions contribute not only to the rapid loss of MeV electrons through EMIC wave-particle interactions while extending the resonance energy to a few MeV by broadening bandwidth via nonlinear wave growth but also to interactions with sub-MeV electrons through the nonresonant effect.

DOI： 10.1029/2024GL113855

Arase In Situ Observations of High-Frequency Electromagnetic Ion Cyclotron (EMIC) Waves in Regions Close to the Earth During the May 2024 Storm Open Access

Jun C.W., Miyoshi Y., Hori T., Kitamura N., Kim K.H., Lee J.H., Bortnik J., Lyons L., Shinohara I., Matsuoka A., Kasahara Y., Matsuda S., Kasaba Y., Teramoto M., Yamamoto K., Shinbori A.

Geophysical Research Letters 52 巻 ( 7 ) 2025年4月

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

During the May 2024 storm, the minimum Dst index was approximately −412 nT, marking the largest geomagnetic storm of the past decade. This event caused the inner edge of the ring current to penetrate deeply into the inner magnetosphere during the main phase of the storm. We present observations of high-frequency electromagnetic ion cyclotron (HF EMIC) wave activity during this intense geomagnetic storm using data from the Arase satellite. Arase observations showed that HF EMIC waves with frequencies of 5–36 Hz at L ∼ 2, occurred mainly during the main and early-recovery phases. The minimum resonance energy of energetic protons and relativistic electrons associated with HF EMIC waves suggests their potential to cause the loss of relativistic electrons in the low L-shell region. Our observations provide new insights into the generation of EMIC waves and the dynamics of energetic particles at low L-shells in the inner magnetosphere.

DOI： 10.1029/2024GL112489

Properties of EMIC Waves and EMIC Wave-Driven Electron Precipitation in Subauroral Latitudes Observed at Athabasca, Canada Open Access

Hirai A., Tsuchiya F., Obara T., Miyoshi Y., Katoh Y., Kasaba Y., Shiokawa K., Kumamoto A., Kasahara Y., Matsuda S., Misawa H., Kurita S., Jun C.W., Ohya H., Connors M.G.

Journal of Geophysical Research: Space Physics 130 巻 ( 3 ) 2025年3月

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

Electromagnetic ion cyclotron (EMIC) waves are believed to cause the loss of relativistic electrons from the outer radiation belt into the atmosphere due to pitch angle scattering. However, it is still unclear whether all EMIC waves can scatter relativistic electrons or which conditions are favorable for pitch angle scattering by EMIC waves. In this study, we performed a 2-year data analysis of EMIC waves and EMIC wave-driven electron precipitation (EP), from 1 November 2016–31 October 2018. Electromagnetic ion cyclotron waves were observed using a ground-based magnetometer installed at Athabasca (ATH, (Formula presented.) 4.3), Canada. Electron precipitation events were identified from very low-frequency radio waves propagated from the transmitters at North Dakota (NDK, (Formula presented.) 3.0) and Seattle (NLK, (Formula presented.) 2.9) stations in USA to the receiver installed at ATH. The magnetic local time dependence of EMIC waves showed higher occurrence rates in the dawn sector. In contrast, EMIC waves accompanied by EP were localized in the dusk sector and were likely to occur during geomagnetic substorms. We found that EMIC waves accompanied by EP were associated with the main phase of geomagnetic storms and occurred inside the plasmapause. These results suggest that the EMIC waves that cause EP occur in the overlap region between the ring current and dense cold plasma during the main phase of geomagnetic storms. This is consistent with previous studies describing that the electron resonant energy with EMIC waves is lower in regions with high plasma density.

DOI： 10.1029/2024JA033357

Statistical Survey of Loss Cone Electrons Observed In Situ in the Inner Magnetosphere Open Access

R. Takahara, I. Shinohara, S. Kasahara, K. Asamura, S. Yokota, K. Keika, Y. Kazama, S.‐Y. Wang, S. W. Y. Tam, T.‐F. Chang, B.‐J. Wang, C.‐W. Jun, T. Hori, A. Matsuoka, M. Teramoto, K. Yamamoto, Y. Kasahara, S. Matsuda, A. Kumamoto, A. Shinbori, F. Tsuchiya, Y. Miyoshi

Geophysical Research Letters 52 巻 ( 3 ) 2025年2月

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

Abstract

We report a statistical result of electrons inside the loss cone with energies of 67 eV–88 keV using electron measurements obtained in situ by the Arase satellite in the inner magnetosphere around the magnetic equator for 60 months. Loss cone electrons are found with a high occurrence probability from the nightside to the dawnside at approximately L = 6. For 641 eV–88 keV electrons, the high‐occurrence region shifts toward later magnetic local times (MLTs) with increasing loss cone electron energy. The spatial distribution of the occurrence probability around MLT = 22–3 at L = 5–6 is consistent with the calculated average resonance energy distribution of whistler mode chorus waves near the magnetic equator. These results suggest that pitch angle scattering driven by chorus waves plays the main role in electron precipitation in this region.

DOI： 10.1029/2024gl112948

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 査読有り Open Access

Sugimura R., Shiokawa K., Otsuka Y., Oyama S.i., Oksanen A., Connors M., Kadokura A., Poddelsky I., Nishitani N., Shepherd S.G., Ruohoniemi J.M., Smith C., Spence H., Reeves G., Funsten H.O., Miyoshi Y., Shinohara I., Kasahara Y., Tsuchiya F., Kumamoto A., Shinbori A., Asamura K., Yokota S., Kazama Y., Jun C.W., Wang S.Y., Tam S.W.Y., Chang T.F., Wang B.J., Kasahara S., Keika K., Hori T., Matsuoka A.

Journal of Geophysical Research: Space Physics 130 巻 ( 2 ) 頁： e2024JA032793 2025年2月

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

Strong Thermal Emission Velocity Enhancement (STEVE) is a latitudinally narrow, purple-band emission observed at subauroral latitudes. Stable Auroral Red (SAR) arcs characterized by major red emission, and red/green arcs with both red and green emissions also occur at subauroral latitudes. Characteristics of magnetospheric source plasma and electromagnetic fields of these three types of arcs have not been fully understood because of the limited conjugate observations between magnetosphere and the ground. In this study, we report 11 conjugate observations (2 STEVEs, 7 SAR arcs, and 2 red/green arcs), using all-sky images obtained at seven ground stations over more than four years from January 2017 to April 2021 and magnetospheric satellites (Arase and Van Allen Probes). We found that, in the inner magnetosphere, the source region of STEVEs and red/green arcs were located outside the plasmasphere, and that of the SAR arc was in the region of spatial overlap between the plasmasphere and ring current region. Electromagnetic waves at frequencies below 1 Hz were observed for STEVEs and red/green arcs. SuperDARN radar data showed a strong westward plasma flow in the ionosphere, especially during STEVE events, whereas the plasma flows associated with SAR arcs and red/green arcs were generally weaker and variable. The STEVE and SAR arc can appear simultaneously at slightly different latitudes and STEVEs and red/green arcs can transform into SAR arcs. These first comprehensive ground-satellite measurements of three types of subauroral-latitude auroras increase our understanding on similarlity, differences, and coupling of these auroras in the ionosphere and the magnetosphere.

DOI： 10.1029/2024ja032793

Properties of EMIC waves and EMIC wave-driven REP observed in subauroral latitudes Open Access

Asuka Hirai, Fuminori Tsuchiya, Takahiro Obara, Yoshizumi Miyoshi, Yuto Katoh, Yasumasa Kasaba, Kazuo Shiokawa, Atsushi Kumamoto, Yoshiya Kasahara, Shoya Matsuda, Hiroaki Misawa, Satoshi Kurita, Chae-Woo Jun, Hiroyo Ohya, Martin Connors

2024年9月

Precipitation of Auroral Electrons Accelerated at Very High Altitudes: Impact on the Ionosphere and a Possible Acceleration Mechanism Open Access

Imajo S., Miyoshi Y., Kazama Y., Asamura K., Shinohara I., Shiokawa K., Kasahara Y., Kasaba Y., Matsuoka A., Wang S.Y., Tam S.W.Y., Chang T.F., Wang B.J., Jun C.W., Teramoto M., Kurita S., Tsuchiya F., Kumamoto A., Saito K., Hori T.

Journal of Geophysical Research: Space Physics 129 巻 ( 9 ) 2024年9月

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

The Arase satellite observed the precipitation of monoenergetic electrons accelerated from a very high altitude above 32,000 km altitude on 16 September 2017. The event was selected in the period when the high-angular resolution channel of the electron detector looked at pitch angles within ∼5° from the ambient magnetic field direction, and thereby was the first to examine the detailed distribution of electron flux near the energy-dependent loss cone at such high altitudes. The potential energy below the satellite estimated from the observed energy-dependence of the loss cone was consistent with the energy of the upgoing ion beams, indicating that ionospheric ions were accelerated by a lower-altitude acceleration region. The accelerated electrons inside the loss cone carried a significant net field-aligned current (FAC) density corresponding to ionospheric-altitude FAC of up to ∼3μA/m2. Based on the anisotropy of the accelerated electrons, we estimated the height of the upper boundary of the acceleration region to be >∼2 RE above the satellite. The height distribution of the acceleration region below the satellite, estimated from the frequency of auroral kilometric radiation, was ∼4,000–13,000 km altitude, suggesting that the very-high-altitude acceleration region was separated from the lower acceleration region. Additionally, we observed time domain structure (TDS) electric fields on a subsecond time scale with a thin FAC indicated by magnetic deflections. Such a TDS may be generated by the formation of double layers in the magnetotail, and its potential drop could significantly contribute (∼40%–60%) to the parallel energization of precipitating auroral electrons.

DOI： 10.1029/2024ja032696

Cold Electron Temperature in the Inner Magnetosphere Estimated Through the Dispersion Relation of ECH Waves From the Arase Satellite Observations Open Access

Taki T., Kurita S., Kojima H., Kasahara Y., Matsuda S., Matsuoka A., Kazama Y., Jun C.W., Wang S.Y., Tam S.W.Y., Chang T.F., Wang B.J., Miyoshi Y., Shinohara I.

Radio Science 59 巻 ( 6 ) 2024年6月

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

We have analyzed Electrostatic Electron Cyclotron Harmonic (ECH) waves observed using interferometry observation mode performed by the Arase satellite to estimate low-energy electron temperatures. Interferometry can be used to calculate velocities, but the Arase satellite can only perform interferometry observations in a one-dimensional direction. We proposed a method to estimate the wave vector of the observed ECH waves from the observed electric fields and calculated the phase velocity for each frequency. We determined the particle parameters from the particle detector and the upper hybrid resonance and estimated the unknown low-energy electron temperature from the agreement between the observed ECH dispersion relation and the theoretical dispersion curves. We performed our analysis for six events and found that the low-energy electron temperature in the observed region is on the order of 1 eV.

DOI： 10.1029/2023rs007927

Modeling the Dynamic Global Distribution of the Ring Current Oxygen Ions Using Artificial Neural Network Technique Open Access

Wang Q., Yue C., Li J., Bortnik J., Ma D., Jun C.W.

Space Weather 22 巻 ( 6 ) 2024年6月

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

The ring current is an important component of the Earth's near-space environment, as its variations are the direct driver of geomagnetic storms that can disrupt power grids, satellite communications, and navigation systems, thereby impacting a wide range of technological and human activities. Oxygen ions (O+) are one of the major components of the ring current and play a significant role in both the enhancement and depletion of the ring current during geomagnetic storms. Although a standard statistical study can provide average global distributions of ring current ions, it can't offer insight into the short-term dynamic variations of the global distribution. Therefore, we employed the Artificial Neural Network technique to construct a global ring current O+ ion model based on the Van Allen Probes observations. Through optimization of the combination of input geomagnetic indices and their respective time history lengths, the model can well reproduce the spatiotemporal variation of the oxygen ion flux distributions and demonstrates remarkable accuracy and minimal errors. Additionally, the model effectively reconstructs the temporal variation of ring current O+ ions for non-training set data. Furthermore, the model provides a comprehensive and dynamic representation of global ring current O+ ion distribution. It accurately captures the dynamics of O+ ions during a geomagnetic storm with the oxygen ion fluxes enhancement and decay, and reveals distinct characteristics for different energy levels, such as injection from the plasma sheet, outflow from the ionosphere, and magnetic local time asymmetry.

DOI： 10.1029/2023SW003779

Global Distribution of EMIC Waves and Its Association to Subauroral Proton Precipitation During the 27 May 2017 Storm: Modeling and Multipoint Observations Open Access

Shreedevi P.R., Yu Y., Miyoshi Y., Tian X., Zhu M., Jordanova V.K., Nakamura S., Jun C.W., Kumar S., Shiokawa K., Connors M., Hori T., Shoji M., Shinohara I., Yokota S., Kasahara S., Keika K., Matsuoka A., Kadokura A., Tsuchiya F., Kumamoto A., Kasahara Y.

Journal of Geophysical Research: Space Physics 129 巻 ( 6 ) 2024年5月

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

Recent simulation studies using the RAM-SCB model showed that proton precipitation contributes significantly to the total energy flux deposited into the subauroral ionosphere thereby affecting the magnetosphere-ionosphere coupling. In this study, we use the BATS-R-US + RAM-SCB model to understand the evolution of ElectroMagnetic Ion Cyclotron (EMIC) waves in the inner magnetosphere, their correspondence to the proton precipitation into the subauroral ionosphere, and to assess the performance of the model in reproducing the EMIC wave-particle interactions. During the 27 May 2017 storm, Arase and RBSP-A satellites observed typical signatures of EMIC waves in the inner magnetosphere. Within this interval, Defense Meteorological Satellite Program (DMSP) and National Oceanic and Atmospheric Administration (NOAA)/MetOp satellites observed significant proton precipitation in the dusk-midnight sector. Simulation results show that H- and He-band EMIC waves are excited within regions of strong temperature anisotropy near the plasmapause. The simulated growth rates of EMIC waves show a similar trend to that of the EMIC wave power observed by the Arase and RBSP-A satellites, suggesting that the model can reproduce the EMIC wave activity qualitatively. The simulated H-band waves in the dusk sector are stronger than He-band waves possibly due to the presence of excess protons in the boundary conditions obtained from the BATS-R-US code. The precipitating proton fluxes reproduced by the simulation with EMIC waves are found to agree reasonably well with the DMSP and NOAA/MetOp satellite observations. It is suggested that EMIC wave scattering of ring current ions can account for proton precipitation observed by the DMSP and MetOp satellites during the 27 May 2017 storm.

DOI： 10.1029/2023ja032337

Observation and Numerical Simulation of Cold Ions Energized by EMIC Waves Open Access

Kim K.H., Jun C.W., Kwon J.W., Lee J., Shiokawa K., Miyoshi Y., Kim E.H., Min K., Seough J., Asamura K., Shinohara I., Matsuoka A., Yokota S., Kasahara Y., Kasahara S., Hori T., Keika K., Kumamoto A., Tsuchiya F.

Journal of Geophysical Research: Space Physics 129 巻 ( 5 ) 2024年5月

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

This is the first report of significant energization (up to 7,000 eV) of low-energy He+ ions, which occurred simultaneously with H-band electromagnetic ion cyclotron (EMIC) wave activity, in a direction mostly perpendicular to the ambient magnetic field. The event was detected by the Arase satellite in the dayside plasmatrough region off the magnetic equator on 15 May 2019. The peak energy of the He+ flux enhancements is mostly above 1,000 eV. At some interval, the He+ ions are energized up to ∼7,000 eV. The H-band waves are excited in a frequency band between the local crossover and helium gyrofrequencies and are close to a linear polarization state with weakly left-handed or right-handed polarization. The normal angle of the waves exhibits significant variation between 0° and 80°, indicating a non-parallel propagation. We run a hybrid code with parameters estimated from the Arase observations to examine the He+ energization. The simulations show that cold He+ ions are energized up to more than 1,000 eV, similar to the spacecraft observations. From the analysis of the simulated wave fields and cold plasma motions, we found that the ratio of the wave frequency to He+ gyrofrequency is a primary factor for transverse energization of cold He+ ions. As a consequence of the numerical analysis, we suggest that the significant transverse energization of He+ ions observed by Arase is attributed to H-band EMIC waves excited near the local helium gyrofrequency.

DOI： 10.1029/2023ja032361

A Triggering Process for Nonlinear EMIC Waves Driven by the Compression of the Dayside Magnetosphere 査読有り Open Access

Jun C.W., Miyoshi Y., Nakamura S., Shoji M., Hori T., Bortnik J., Lyons L., Shinohara I., Matsuoka A.

Geophysical Research Letters 51 巻 ( 1 ) 2024年1月

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

Using the Arase and Van Allen Probes satellite observations, we investigate the nonlinear electromagnetic ion cyclotron (EMIC) rising-tone (RT) emissions with an increase of the solar wind dynamic pressure in the dayside magnetosphere. We find that EMIC RT emissions are accompanied by the extended dayside uniform zone (DUZ) over |MLAT| < 25° due to the dayside magnetospheric compression by an increase in Pdyn. Using the observed plasma and magnetic field data, we modeled the threshold amplitude for the nonlinear EMIC waves and compared it with the observation. The small gradient of the ambient magnetic field strongly contributes to the reduction in the threshold amplitude of nonlinear wave growth compared to other parameters. When the threshold amplitude falls to comparable level of pre-existing EMIC waves, EMIC RT emissions are immediately triggered, suggesting direct evidence that the DUZ is the preferred condition to cause the nonlinear EMIC RT emission in the dayside magnetosphere.

DOI： 10.1029/2023GL106860

Correspondence of Pi2 Pulsations, Aurora Luminosity, and Plasma Flux Fluctuation Near a Substorm Brightening Aurora: Arase Observations

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

Journal of Geophysical Research: Space Physics 128 巻 ( 10 ) 2023年9月

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

Although many substorm-related observations have been made, we still have limited insight into propagation of the plasma and field perturbations in Pi2 frequencies (∼7–25 mHz) in association with substorm aurora, particularly from the auroral source region in the inner magnetosphere to the ground. In this study, we present conjugate observations of a substorm brightening aurora using an all-sky camera and an inner-magnetospheric satellite Arase at L ∼ 5. A camera at Gakona (62.39°N, 214.78°E), Alaska, observed a substorm auroral brightening on 28 December 2018, and the footprint of the satellite was located just equatorward of the aurora. Around the timing of the auroral brightening, the satellite observed a series of quasi-periodic variations in the electric and magnetic fields and in the energy flux of electrons and ions. We demonstrate that the diamagnetic variations of thermal pressure and medium-energy ion energy flux in the inner magnetosphere show approximately one-to-one correspondence with the oscillations in luminosity of the substorm brightening aurora and high-latitudinal Pi2 pulsations on the ground. We also found their anti-correlation with low-energy electrons. Cavity-type Pi2 pulsations were observed at mid- and low-latitudinal stations. Based on these observations, we suggest that a wave phenomenon in the substorm auroral source region, like ballooning type instability, play an important role in the development of substorm and related auroral brightening and high-latitude Pi2, and that the variation of the auroral luminosity was directly driven by keV electrons which were modulated by Alfven waves in the inner magnetosphere.

DOI： 10.1029/2023ja031648

Plasma Pressure Distribution of Ions and Electrons in the Inner Magnetosphere During CIR Driven Storms Observed During Arase Era Open Access

Kumar S., Miyoshi Y., Jordanova V.K., Kistler L.M., Park I., Jun C., Hori T., Asamura K., Shreedevi P.R., Yokota S., Kasahara S., Kazama Y., Wang S.Y., Tam S.W.Y., Chang T.F., Mitani T., Higashio N., Keika K., Matsuoka A., Imajo S., Shinohara I.

Journal of Geophysical Research: Space Physics 128 巻 ( 9 ) 2023年9月

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

Using Arase observations of the inner magnetosphere during 26 CIR-driven geomagnetic storms with minimum Sym-H between −33 and −86 nT, we investigated ring current pressure development of ions (H+, He+, O+) and electron during prestorm, main, early recovery and late recovery phases as a function of L-shell and magnetic local time. It is found that during the main and early recovery phase of the storms the ion pressure is asymmetric in the inner magnetosphere, leading to a strong partial ring current. The ion pressure becomes symmetric during the late recovery phase. H+ ions with energies of ∼20–50 keV and ∼50–100 keV contribute more to the ring current pressure during the main phase and early/late recovery phase, respectively. O+ ions with energies of ∼10–20 keV contribute significantly during main and early recovery phase. These are consistent with previous studies. The electron pressure was found to be asymmetric during the main, early recovery and late recovery phase. The electron pressure peaks from midnight to the dawn sector. Electrons with energy of <50 keV contribute to the ring current pressure during the main and early recovery phase of the storms. Overall, the electron contribution to the total ring current is found to be ∼11% during the main and early recovery phases. However, the electron contribution is found to be significant (∼22%) in the 03–09 MLT sector during the main and early recovery phase. The results indicate an important role of electrons in the ring current build up.

DOI： 10.1029/2023ja031756

An Implication of Detecting the Internal Modulation in a Pulsating Aurora: A Conjugate Observation by the Arase Satellite and All-Sky Imagers

Nanjo S., Ebukuro S., Nakamura S., Miyoshi Y., Kurita S., Oyama S.I., Ogawa Y., Keika K., Kasahara Y., Kasahara S., Matsuoka A., Hori T., Yokota S., Matsuda S., Shinohara I., Wang S.Y., Kazama Y., Jun C.W., Kitahara M., Hosokawa K.

Journal of Geophysical Research: Space Physics 128 巻 ( 8 ) 2023年8月

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

A physical mechanism to produce pulsating aurora (PsA) has been considered to be the interaction of the electron and the chorus wave generated near the equatorial plane of the magnetosphere. A recent observation of high temporal resolution of chorus waves by the Arase satellite revealed that the presence or absence of the internal modulation of PsA, which is a characteristic sub-second scintillation at 3 ± 1 Hz within each optical pulsation, is closely related to the discreteness of the element structure of the chorus wave. However, it is still unclear what parameters (or conditions) control the discreteness of the element and the existence of the internal modulation of PsA. In this study, we discuss parameters that determine the presence or absence of the internal modulation of PsA and element structure of chorus by showing a conjugate observation of PsA/chorus by ground-based cameras and the Arase satellite. During the event, the occurrence of internal modulation increased temporally. The wave data from the satellite show that the repetitive frequency of elements was ∼6 Hz when the internal modulation was indistinct, while the repetitive frequency was ∼3 Hz when the internal modulation was distinct. The particle measurements suggest that this difference was caused by changes in the density and the temperature anisotropy of the hot electron. The internal modulation was clearly observed when the density of hot electrons decreased and the temperature anisotropy relaxed after the injection. Observations of internal modulations from the ground might allow us to estimate the parameters such as energetic electron density and temperature anisotropy in the magnetosphere.

DOI： 10.1029/2023ja031499

Spatio-Temporal Characteristics of IPDP-Type EMIC Waves on April 19, 2017: Implications for Loss of Relativistic Electrons in the Outer Belt Open Access

Hirai A., Tsuchiya F., Obara T., Katoh Y., Miyoshi Y., Shiokawa K., Kasaba Y., Misawa H., Jun C.W., Kurita S., Connors M.G., Hendry A.T., Shinbori A., Otsuka Y., Tsugawa T., Nishioka M., Perwitasari S., Manweiler J.W.

Journal of Geophysical Research: Space Physics 128 巻 ( 8 ) 2023年8月

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

To understand the mechanism of the increased frequency of intervals of pulsations of diminishing periods (IPDPs), we analyzed IPDP-type electromagnetic ion cyclotron (EMIC) waves that occurred on 19 April 2017, using ground and satellite observations. Observations by low-altitude satellites and ground-based magnetometers indicate that the increased IPDP frequency is caused by an inward (i.e., Earthward) shift of the EMIC wave source region. The EMIC wave source region moves inward along the mid-latitude trough, which we used as a proxy for the plasmapause location. A statistical analysis shows that increases in the IPDP frequency showed a positive correlation with polar cap potentials. These results suggest an enhanced convection electric field causes an inward shift of the source region. The inward shift of the source region allows EMIC waves to scatter relativistic electrons over a wide range of radial distances during the IPDP event. This mechanism suggests that IPDP-type EMIC waves are more likely to scatter relativistic electrons than other EMIC waves. We also show that the decreased phase-space density of relativistic electrons in the outer radiation belt is consistent with the extent of the source region and the resonant energy of EMIC waves, implying a possible contribution of EMIC waves to outer radiation belt loss during the main phase of geomagnetic storms.

DOI： 10.1029/2023JA031479

Statistical Study of EMIC Waves and Related Proton Distributions Observed by the Arase Satellite

Jun C.W., Miyoshi Y., Nakamura S., Shoji M., Kitahara M., Hori T., Yue C., Bortnik J., Lyons L., Min K., Kasahara Y., Tsuchiya F., Kumamoto A., Asamura K., Shinohara I., Matsuoka A., Imajo S., Yokota S., Kasahara S., Keika K.

Journal of Geophysical Research: Space Physics 128 巻 ( 6 ) 2023年5月

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

We performed a statistical study of electromagnetic ion cyclotron (EMIC) wave distributions and their coupling with energetic protons in the inner magnetosphere using the Arase satellite data from May 2017 to December 2020. We investigated the energetic proton pitch-angle distributions and partial thermal pressures associated with EMIC waves using inter-calibrated proton data in the energy range of 30 eV/q–187 keV/q. With a cold plasma approximation, we computed the proton minimum resonance energies using the observed EMIC wave frequency and plasma density values. We found that the EMIC waves had left-handed polarization near the magnetic equator close to the threshold of proton cyclotron instability, and propagated to higher latitudes along the field line with polarization reversal. H-EMIC waves showed two peak occurrence regions in the morning and noon sectors at L = 7.5–9 outside the plasmasphere. The flux enhancements associated with morning side H-EMIC waves appeared at E < 1 keV/q among all pitch angles, while H-EMIC waves in the noon sector exhibited flux enhancement in field-aligned directions at E = 1–100 keV/q. He-EMIC waves showed a broad occurrence region from 12 to 20 magnetic local time at L = 5.5–8.5 inside the plasmasphere with strong flux enhancements at all pitch-angle ranges at E = 1–100 keV/q. The proton minimum resonance energy using the obtained central frequency was consistent with the observed flux enhancements at different peak occurrence regions. We conclude that the free energy sources of EMIC waves in different geomagnetic environments drive various types of EMIC waves, and they interact with energetic protons at different energy ranges.

DOI： 10.1029/2022ja031131

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

Liu J., Shiokawa K., Oyama S.I., Otsuka Y., Jun C.W., Nosé 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

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

Pc1 geomagnetic pulsations correspond to electromagnetic ion cyclotron (EMIC) waves in the magnetosphere and are excited there with frequencies of 0.2–5 Hz. The instantaneous longitudinal extent of Pc1 waves on the ground has not been estimated yet. In this study, we analyze the Pc1 pulsations observed at seven longitudinally-distributed ground stations at subauroral latitudes at ∼60° magnetic latitude for 1 year from July 2018 to June 2019. The hourly occurrence rates of Pc1 pulsations at all 7 stations have a peak (14%–39.6%) in the post-noon sector and a local minimum (4.1%–8.1%) at midnight. The average frequencies become highest (0.6–1.1 Hz) after midnight and lowest (0.3–0.5 Hz) after noon at all 7 stations. An increasing tendency of total Pc1 occurrence with respect to magnetic latitude was observed. Based on these observations, we obtained a peak of probability distribution of the instantaneous Pc1 longitudinal extent as ∼82.5° with a half maximum at ∼114°, though this probability distribution can be affected by the limitation of the number of the stations. We also made model calculations on the possible longitudinal extent using artificial random Pc1 waves with fixed extents. The comparison of the model results with the observation suggests longitudinal extent of 70°–86° comparable to the peak of probability distribution (∼82.5°). A superposed epoch analysis shows that the longitudinal extent of Pc1 waves tends to increase during recovery phase of geomagnetic storms.

DOI： 10.1029/2021ja029987

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JA029987

Observation of Source Plasma and Field Variations of a Substorm Brightening Aurora at L ∼ 6 by a Ground-Based Camera and the Arase Satellite on 12 October 2017 査読有り

Chen L., Shiokawa K., Miyoshi Y., Oyama S., Jun C.W., Ogawa Y., Hosokawa K., Inaba Y., Kazama Y., Wang S.Y., Tam S.W.Y., Chang T.F., Wang B.J., Asamura K., Kasahara S., Yokota S., Hori T., Keika K., Kasaba Y., Kumamoto A., Tsuchiya F., Shoji M., Kasahara Y., Matsuoka A., Shinohara I., Imajo S., Nakamura S., Kitahara M.

Journal of Geophysical Research: Space Physics 127 巻 ( 11 ) 2022年10月

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

Auroral brightening is one of the most common phenomena that occur during substorm onset and is usually recognized as a projection of the substorm-associated magnetospheric plasma dynamics to the ionosphere. However, electromagnetic fields and plasma features associated with the substorm brightening arc have not been well understood. In this study, we present a comprehensive observation of the source plasma and field variations of a substorm brightening aurora in the inner magnetosphere. We performed a unique conjugate observation of a substorm brightening auroral arc observed by a ground-based camera and by the Arase satellite in the magnetospheric source region at L ∼ 6. The event was observed at Tromsø (69.6°N, 19.2°E), Norway, on 12 October 2017. The brightening arc indicates east-west structures with longitudinal scales of ∼0.5°–2.0°. Field-aligned bi-directional electrons with an energy range between 66 and 1,800 eV were detected by the satellite, simultaneously with the appearance of the brightening arc in the camera. These electrons were probably supplied from the auroral brightening region in the ionosphere, indicating that the satellite was on the same field line of the brightening aurora. The magnetic and electric field data show characteristic fluctuations and earthward Poynting flux around the time that the satellite crossed the aurora. Anti-phase oscillations between the thermal pressure and the magnetic pressure are also reported. Based on these observations, we suggest the possibility that a ballooning instability occurred in the source region of the substorm brightening arc in the inner magnetosphere at L ∼ 6.

DOI： 10.1029/2021ja030072

The Space Physics Environment Data Analysis System in Python Open Access

Grimes E.W., Harter B., Hatzigeorgiu N., Drozdov A., Lewis J.W., Angelopoulos V., Cao X., Chu X., Hori T., Matsuda S., Jun C.W., Nakamura S., Kitahara M., Segawa T., Miyoshi Y., Le Contel O.

Frontiers in Astronomy and Space Sciences 9 巻 2022年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Frontiers in Astronomy and Space Sciences

In this article, we describe the free, open-source Python-based Space Physics Environment Data Analysis System (PySPEDAS), a platform for multi-mission, multi-instrument retrieval, analysis, and visualization of Heliophysics data. PySPEDAS currently contains load routines for data from 23 space missions, as well as a variety of data from ground-based observatories. The load routines are built from a common set of general routines that provide access to datasets in different ways (e.g., downloading and caching CDF files or accessing data hosted on web services), making the process of adding additional datasets simple. In addition to load routines, PySPEDAS contains numerous analysis tools for working with the dataset once it is loaded. We describe how these load routines and analysis tools are built by utilizing other free, open-source Python projects (e.g., PyTplot, cdflib, hapiclient, etc.) to make tools for space and solar physicists that are extremely powerful, yet easy-to-use. After discussing the code in detail, we show numerous examples of code using PySPEDAS, and discuss limitations and future plans.

DOI： 10.3389/fspas.2022.1020815

Analysis of Electron Precipitation and Ionospheric Density Enhancements Due To Hiss Using Incoherent Scatter Radar and Arase Observations

Ma Q., Xu W., Sanchez E.R., Marshall R.A., Bortnik J., Reyes P.M., Varney R.H., Kaeppler S.R., Miyoshi Y., Matsuoka A., Kasahara Y., Matsuda S., Tsuchiya F., Kumamoto A., Kasahara S., Yokota S., Keika K., Hori T., Mitani T., Nakamura S., Kazama Y., Wang S.Y., Jun C.W., Shinohara I., Tam S.W.Y.

Journal of Geophysical Research: Space Physics 127 巻 ( 8 ) 2022年8月

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

Plasmaspheric hiss can cause energetic electron precipitation from the magnetosphere to the Earth's upper atmosphere and affect the ionospheric electron density profiles. In this study, we use Arase satellite measurements in the dayside plasmasphere to model the electron precipitation and the resultant ionospheric response, and compare the results to the electron density measured by the Poker Flat Incoherent Scatter Radar (PFISR). We analyzed two close conjunction events between Arase and PFISR at L ∼ 6 in the afternoon sector, when Arase was in the outer plasmasphere and traveled into the plasmaspheric plumes. Modest or strong hiss waves were observed with amplitudes higher than 50 pT during both events. Quasilinear modeling suggests that the hiss waves could cause intense electron precipitation ranging from several keV to several hundred keV energies. The electron density profiles at 60–90 km modeled by the Boulder Electron Radiation to Ionization (BERI) model suggest significant electron density enhancements due to the precipitating electrons. PFISR simultaneously observed electron density enhancements during both events, and provided evidence for the electron precipitation at altitudes down to <70 km. The temporal modulation of hiss caused the modulated density profiles in BERI modeling, but was not evident in PFISR observations. The modeled altitude profiles of the perturbed electron density overall agree with PFISR observation. At altitudes below 75 km, the modeled electron densities are lower than the observation, suggesting additional high energy electron precipitation possibly due to low frequency (<50 Hz) waves or hiss wave powers ducted to high latitudes.

DOI： 10.1029/2022ja030545

Statistical Survey of Arase Satellite Data Sets in Conjunction With the Finnish Riometer Network Open Access

Thomas N., Kero A., Miyoshi Y., Shiokawa K., Hyötylä M., Raita T., Kasahara Y., Shinohara I., Matsuda S., Nakamura S., Kasahara S., Yokota S., Keika K., Hori T., Mitani T., Takashima T., Asamura K., Kazama Y., Wang S.Y., Jun C.W., Higashio N.

Journal of Geophysical Research: Space Physics 127 巻 ( 5 ) 2022年4月

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

During disturbed geomagnetic conditions, the energetic particles in the inner magnetosphere are known to undergo precipitation loss due to interaction with various plasma waves. This study, investigates the energetic particle precipitation events statistically using coordinate observations from the ground riometer network and the inner-magnetospheric satellite mission, Arase. We have compared cosmic noise absorption (CNA) data obtained from the Finnish ground riometer network located in the auroral/sub-auroral latitudes with the comprehensive data set of omnidirectional electron/proton flux and plasma waves in ELF/VLF frequency range from the Arase satellite during the overpass intervals. The study period includes one and a half years of data between March 2017 and September 2018 covering Arase conjunctions with the riometer stations from all magnetic local time sectors. The relation between the plasma flux/waves observed at the satellite with the riometer absorptions are investigated statistically for CNA (absorption >0.5 dB) and non-CNA (absorption <0.5 dB) cases separately. During CNA events, Arase observed elevated electron flux in the medium energy range (2–100 keV), and plasma wave activity in the whistler-mode frequency range (0.5–3 kHz) of the spectra. Our study provides an estimate of the statistical dependence of the electron flux and plasma wave observations at Arase with the ground reality of actual precipitation.

DOI： 10.1029/2022ja030271

Statistical Study of Approaching Strong Diffusion of Low-Energy Electrons by Chorus and ECH Waves Based on In Situ Observations

Fukizawa M., Sakanoi T., Miyoshi Y., Kazama Y., Katoh Y., Kasahara Y., Matsuda S., Kumamoto A., Tsuchiya F., Matsuoka A., Kurita S., Nakamura S., Shoji M., Teramoto M., Imajo S., Shinohara I., Wang S.Y., Tam S.W.Y., Chang T.F., Wang B.J., Jun C.W.

Journal of Geophysical Research: Space Physics 127 巻 ( 3 ) 2022年3月

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

Inner magnetospheric electrons are precipitated in the ionosphere via pitch-angle (PA) scattering by lower band chorus (LBC), upper band chorus (UBC), and electrostatic electron cyclotron harmonic (ECH) waves. However, the PA scattering efficiency of low-energy electrons (0.1–10 keV) has not been investigated via in situ observations because of difficulties in flux measurements within loss cones at the magnetosphere. In this study, we demonstrate that LBC, UBC, and ECH waves contribute to PA scattering of electrons at different energy ranges using the Arase (ERG) satellite observation data and successively detected the moderate loss cone filling, that is, approaching strong diffusion. Approaching strong diffusion by LBC, UBC, and ECH waves occurred at ∼2–20 keV, ∼1–10 keV, and ∼0.1–2 keV, respectively. The occurrence rate of the approaching strong diffusion by high-amplitude LBC (>50 pT), UBC (>20 pT), and ECH (>10 mV/m) waves, respectively, reached ∼70%, ∼40%, and ∼30% higher than that without simultaneous wave activity. The energy range in which the occurrence rate was high agreed with the range where the PA diffusion rate of each wave exceeded the strong diffusion level based on the quasilinear theory.

DOI： 10.1029/2022ja030269

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022JA030269

Unusual high frequency EMIC waves: Detailed analysis of EMIC wave excitation and energy coupling between EMIC and magnetosonic waves Open Access

Min K., Kim J., Ma Q., Jun C.W., Liu K.

Advances in Space Research 69 巻 ( 1 ) 頁： 35 - 47 2022年1月

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

A recent event study suggested a coupling process whereby suprathermal protons (10–100 eV), as a result of perpendicular heating by pre-existing magnetosonic waves, can excite electromagnetic ion cyclotron (EMIC) waves with frequency near the local proton cyclotron frequency (f~0.95fcp). The present study tests this coupling process. First, one-dimensional hybrid (kinetic ions/massless fluid electrons) simulations of parallel-propagating EMIC waves initialized with the plasma conditions derived from the event prove that high frequency EMIC waves can be generated by anisotropic suprathermal protons instead of more energetic (10s of keV) ring current protons. Calculation of the quasilinear pitch-angle diffusion coefficient for electrons using the simulated waves suggests that these high frequency EMIC waves outside the plasmasphere can play a role in the pitch-angle scattering of ~MeV electrons due to the large wavenumber of the excited EMIC waves. Second, the role of the pre-existing magnetosonic waves in the suprathermal proton heating is examined using quasilinear diffusion theory and simple test particle calculation. It is found that the quasilinear diffusion becomes ineffective in energies relevant to the suprathermal protons, indicating that the low-energy (<10 eV) protons cannot be efficiently energized to the observed level through multi-harmonic cyclotron resonances with the magnetosonic waves observed. Rather, some kind of non-resonant process may have been at play, if the magnetosonic waves were actually involved in the heating. This result suggests that more quantitative understanding of the suggested energy coupling process through magnetosonic waves is needed.

DOI： 10.1016/j.asr.2021.07.039

Collaborative Research Activities of the Arase and Van Allen Probes. Open Access

Miyoshi Y, Shinohara I, Ukhorskiy S, Claudepierre SG, Mitani T, Takashima T, Hori T, Santolik O, Kolmasova I, Matsuda S, Kasahara Y, Teramoto M, Katoh Y, Hikishima M, Kojima H, Kurita S, Imajo S, Higashio N, Kasahara S, Yokota S, Asamura K, Kazama Y, Wang SY, Jun CW, Kasaba Y, Kumamoto A, Tsuchiya F, Shoji M, Nakamura S, Kitahara M, Matsuoka A, Shiokawa K, Seki K, Nosé M, Takahashi K, Martinez-Calderon C, Hospodarsky G, Colpitts C, Kletzing C, Wygant J, Spence H, Baker DN, Reeves GD, Blake JB, Lanzerotti L

Space science reviews 218 巻 ( 5 ) 頁： 38 2022年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Space Science Reviews

This paper presents the highlights of joint observations of the inner magnetosphere by the Arase spacecraft, the Van Allen Probes spacecraft, and ground-based experiments integrated into spacecraft programs. The concurrent operation of the two missions in 2017–2019 facilitated the separation of the spatial and temporal structures of dynamic phenomena occurring in the inner magnetosphere. Because the orbital inclination angle of Arase is larger than that of Van Allen Probes, Arase collected observations at higher L-shells up to L∼ 10. After March 2017, similar variations in plasma and waves were detected by Van Allen Probes and Arase. We describe plasma wave observations at longitudinally separated locations in space and geomagnetically-conjugate locations in space and on the ground. The results of instrument intercalibrations between the two missions are also presented. Arase continued its normal operation after the scientific operation of Van Allen Probes completed in October 2019. The combined Van Allen Probes (2012-2019) and Arase (2017-present) observations will cover a full solar cycle. This will be the first comprehensive long-term observation of the inner magnetosphere and radiation belts.

DOI： 10.1007/s11214-022-00885-4

Study of an Equatorward Detachment of Auroral Arc From the Oval Using Ground-Space Observations and the BATS-R-US–CIMI Model Open Access

Yadav S., Shiokawa K., Oyama S., Inaba Y., Takahashi N., Seki K., Keika K., Chang T.F., Tam S.W.Y., Wang B.J., Kazama Y., Wang S.Y., Asamura K., Kasahara S., Yokota S., Hori T., Kasaba Y., Tsuchiya F., Kumamoto A., Shoji M., Kasahara Y., Matsuoka A., Matsuda S., Jun C.W., Imajo S., Miyoshi Y., Shinohara I.

Journal of Geophysical Research: Space Physics 126 巻 ( 12 ) 2021年12月

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

We present observations of an equatorward detachment of the auroral arc from the main oval and magnetically conjugate measurements made by the Arase satellite in the inner magnetosphere. The all-sky imager at Gakona (magnetic latitude = 63.6°N), Alaska, shows the detachment of the auroral arc in both red and green lines at local midnight (∼0130–0230 MLT) on 30 March 2017. The electron density derived from the Arase in-situ observations shows that this arc occurred outside the plasmapause. At the arc crossing, the electron flux of energies ∼0.1–2 keV is found to be locally enhanced at L∼4.3–4.5. We estimated auroral intensities for both red and green lines by using the Arase low-energy (0.1–19 keV) electron flux data. The peak latitude of the estimated intensity shows reasonably good correspondence with the observed intensity mapped at the ionospheric footprints of the Arase satellite. These findings indicate that the observed arc detachment at Gakona was associated with the localized enhancement of low-energy electrons (∼0.1–2 keV) at the inner edge of the electron plasma sheet. Further, we employ the simulation results of the Community Coordinated Modeling Center (CCMC), the BATS-R-US–CIMI 3-D MHD code to understand the conditions in the inner magnetosphere around the time of detachment. Although the simulation could not reproduce the lower-energy component responsible for the arc detachment, it successfully reproduced two earthward convection events at the lower radial distance (R) (R ≤ ∼4) around the time of arc detachment and the features of enhanced convection in similarity with the observations.

DOI： 10.1029/2020JA029080

Correction to: ISEE_Wave: interactive plasma wave analysis tool (Earth, Planets and Space, (2021), 73, 1, (110), 10.1186/s40623-021-01430-3) Open Access

Matsuda S., Miyoshi Y., Nakamura S., Kitahara M., Shoji M., Hori T., Imajo S., Jun C.W., Kurita S., Kasahara Y., Matsuoka A., Shinohara I.

Earth, Planets and Space 73 巻 ( 1 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth, Planets and Space

After publication of this article (Matsuda et al. 2021), it is noticed the 8th author’s name is incorrect. The name should be corrected from “Jun Chae-Woo” to “Chae-Woo Jun”. The name has been revised in this Correction and the original article has been updated as well.

DOI： 10.1186/s40623-021-01450-z

ISEE_Wave: interactive plasma wave analysis tool

Shoya Matsuda, Yoshizumi Miyoshi, Satoko Nakamura, Masahiro Kitahara, Masafumi Shoji, Tomoaki Hori, Shun Imajo, Jun Chae-Woo, Satoshi Kurita, Yoshiya Kasahara, Ayako Matsuoka, Iku Shinohara

Earth, Planets and Space 73 巻 ( 1 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Springer Science and Business Media LLC

<title>Abstract</title>We have developed ISEE_Wave (Institute for Space-Earth Environmental Research, Nagoya University - Plasma Wave Analysis Tool), an interactive plasma wave analysis tool for electric and magnetic field waveforms observed by the plasma wave experiment aboard the Arase satellite. ISEE_Wave provides an integrated wave analysis environment on a graphical user interface, where users can visualize advanced wave properties, such as the electric and magnetic field wave power spectra, wave normal polar angle, polarization ellipse, planarity of polarization, and Poynting vector angle. Users can simply select a time interval for their analysis, and ISEE_Wave automatically downloads the waveform data, ambient magnetic field data, and spacecraft attitude data from the data archive repository of the ERG Science Center, and then performs necessary coordinate transformation and spectral matrix calculation. The singular value decomposition technique is used as the core technique for the wave property analysis of ISEE_Wave. On-demand analysis is possible by specifying the parameters of the wave property analysis as well as the plot styles using the graphical user interface of ISEE_Wave. The results can be saved as image files of plots and/or a tplot save file. ISEE_Wave aids in the identification of fine structures of observed plasma waves, wave mode identification, and wave propagation analysis. These properties can be used to understand plasma wave generation, propagation, and wave-particle interaction in the inner magnetosphere. ISEE_Wave can also be applied to general waveform data observed by other spacecraft by using the plug-in procedures to load the data.

DOI： 10.1186/s40623-021-01430-3

その他リンク： https://link.springer.com/article/10.1186/s40623-021-01430-3/fulltext.html

Magnetic Field and Energetic Particle Flux Oscillations and High-Frequency Waves Deep in the Inner Magnetosphere During Substorm Dipolarization: ERG Observations Open Access

Miyashita Y., Chang T.F., Miyoshi Y., Hori T., Kadokura A., Kasahara S., Wang S.Y., Keika K., Matsuoka A., Tanaka Y., Kasahara Y., Teramoto M., Jun C.W., Asamura K., Kazama Y., Tam S.W.Y., Wang B.J., Yokota S., Kumamoto A., Tsuchiya F., Shoji M., Kurita S., Imajo S., Shinohara I.

Journal of Geophysical Research: Space Physics 126 巻 ( 9 ) 2021年9月

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

Using Exploration of energization and Radiation in Geospace (ERG or Arase) spacecraft data, we studied low-frequency magnetic field and energetic particle flux oscillations and high-frequency waves deep in the inner magnetosphere at a radial distance of ~4–5 (Formula presented.) during substorm dipolarization. The magnetic field oscillated alternately between dipole-like and taillike configuration at a period of (Formula presented.) 1 min during dipolarization. When the magnetic field was dipole-like, the parallel magnetic component of the Pi2 waves was at trough. Both energetic ion and electron fluxes with a few to tens of kiloelectronvolts enhanced out of phase, indicating that magnetosonic waves were in slow mode. Field-aligned currents also oscillated. These observations are consistent with signatures of ballooning instability. In addition, we found that broadband waves from the Pi1 range to above the electron cyclotron frequency tended to appear intermittently in the central plasma sheet near dipole-like configuration.

DOI： 10.1029/2020ja029095

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029095

First Simultaneous Observation of a Night Time Medium-Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite Open Access

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

Journal of Geophysical Research: Space Physics 126 巻 ( 9 ) 2021年9月

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

Medium-scale traveling ionospheric disturbances (MSTIDs) are a phenomenon widely and frequently observed over the ionosphere from high to low latitudes. Night time MSTIDs are caused generally by the polarization electric field in the ionosphere. However, propagation of this polarization electric field to the magnetosphere has not yet been identified. Here, we report the first observation of the polarization electric field and associated density variations of a night time MSTID in the magnetosphere. The MSTID event was observed by an all-sky airglow imager at Gakona (geographical latitude: 62.39°N, geographical longitude: 214.78°E, magnetic latitude: 63.20°N), Alaska. The Arase satellite passed over the MSTID in the inner magnetosphere at 0530–0800 UT (2030–2300 LT) on November 3, 2018. This MSTID, observed in 630 nm airglow images, was propagating westward with a horizontal wavelength of ∼165 km, a north–south phase front, and a phase velocity of ∼80 m/s. The Arase satellite footprint on the ionosphere crossed the MSTID in the direction nearly perpendicular to the MSTID phase fronts. The electric field and electron density observed by the Arase satellite showed periodic variation associated with the MSTID structure with amplitudes of ∼2 mV/m and ∼150 cm−3, respectively. The electric field variations projected to the ionosphere are mainly in the east-west direction and are consistent with the direction of the polarization electric field expected from MSTID growth by E × B drift. This observation indicates that the polarization electric field associated with the MSTID in the ionosphere is projected onto the magnetosphere, causing plasma density fluctuations in the magnetosphere.

DOI： 10.1029/2020JA029086

Penetration of MeV electrons into the mesosphere accompanying pulsating aurorae. Open Access

Miyoshi Y, Hosokawa K, Kurita S, Oyama SI, Ogawa Y, Saito S, Shinohara I, Kero A, Turunen E, Verronen PT, Kasahara S, Yokota S, Mitani T, Takashima T, Higashio N, Kasahara Y, Matsuda S, Tsuchiya F, Kumamoto A, Matsuoka A, Hori T, Keika K, Shoji M, Teramoto M, Imajo S, Jun C, Nakamura S

Scientific reports 11 巻 ( 1 ) 頁： 13724 - 13724-9 2021年7月

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

Pulsating aurorae (PsA) are caused by the intermittent precipitations of magnetospheric electrons (energies of a few keV to a few tens of keV) through wave-particle interactions, thereby depositing most of their energy at altitudes ~ 100 km. However, the maximum energy of precipitated electrons and its impacts on the atmosphere are unknown. Herein, we report unique observations by the European Incoherent Scatter (EISCAT) radar showing electron precipitations ranging from a few hundred keV to a few MeV during a PsA associated with a weak geomagnetic storm. Simultaneously, the Arase spacecraft has observed intense whistler-mode chorus waves at the conjugate location along magnetic field lines. A computer simulation based on the EISCAT observations shows immediate catalytic ozone depletion at the mesospheric altitudes. Since PsA occurs frequently, often in daily basis, and extends its impact over large MLT areas, we anticipate that the PsA possesses a significant forcing to the mesospheric ozone chemistry in high latitudes through high energy electron precipitations. Therefore, the generation of PsA results in the depletion of mesospheric ozone through high-energy electron precipitations caused by whistler-mode chorus waves, which are similar to the well-known effect due to solar energetic protons triggered by solar flares.

DOI： 10.1038/s41598-021-92611-3

The Characteristics of EMIC Waves in the Magnetosphere Based on the Van Allen Probes and Arase Observations

Jun C.W., Miyoshi Y., Kurita S., Yue C., Bortnik J., Lyons L., Nakamura S., Shoji M., Imajo S., Kletzing C., Kasahara Y., Kasaba Y., Matsuda S., Tsuchiya F., Kumamoto A., Matsuoka A., Shinohara I.

Journal of Geophysical Research: Space Physics 126 巻 ( 6 ) 2021年6月

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

We performed a comprehensive statistical study of electromagnetic ion cyclotron (EMIC) waves observed by the Van Allen Probes and Exploration of energization and Radiation in Geospace satellite (ERG/Arase). From 2017 to 2018, we identified and categorized EMIC wave events with respect to wavebands (H+ and He+ EMIC waves) and relative locations from the plasmasphere (inside and outside the plasmasphere). We found that H+ EMIC waves in the morning sector at L > 8 are predominantly observed with a mixture of linear and right-handed polarity and higher wave normal angles during quiet geomagnetic conditions. Both H+ and He+ EMIC waves observed in the noon sector at L ∼ 4–6 have left-handed polarity and lower wave normal angles at |MLAT| < 20° during the recovery phase of a storm with moderate solar wind pressure. In the afternoon sector (12–18 MLT), He+ EMIC waves are dominantly observed with strongly enhanced wave power at L ∼ 6–8 during the storm main phase, while in the dusk sector (17–21 MLT) they have lower wave normal angles with linear polarity at L > 8 during geomagnetic quiet conditions. Based on distinct characteristics at different EMIC wave occurrence regions, we suggest that EMIC waves in the magnetosphere can be generated by different free energy sources. Possible sources include the freshly injected particles from the plasma sheet, adiabatic heating by dayside magnetospheric compressions, suprathermal proton heating by magnetosonic waves, and off-equatorial sources.

DOI： 10.1029/2020JA029001

Contribution of Electron Pressure to Ring Current and Ground Magnetic Depression Using RAM-SCB Simulations and Arase Observations During 7–8 November 2017 Magnetic Storm Open Access

Kumar S., Miyoshi Y., Jordanova V.K., Engel M., Asamura K., Yokota S., Kasahara S., Kazama Y., Wang S.Y., Mitani T., Keika K., Hori T., Jun C., Shinohara I.

Journal of Geophysical Research: Space Physics 126 巻 ( 6 ) 2021年6月

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

Understanding the physical processes that control the dynamics of energetic particles in the inner magnetosphere is important for both space-borne and ground-based assets essential to the modern society. The storm time distribution of ring current particles in the inner magnetosphere depends strongly on their transport in the evolving electric and magnetic fields along with particle acceleration and loss. In this study, we investigated the ring current particle variations using observations and simulations. We compared the ion (H+, He+, and O+) and electron flux and plasma pressure variations from Arase observations with the self-consistent inner magnetosphere model: Ring current Atmosphere interactions Model with Self Consistent magnetic field (RAM-SCB) during the 7–8 November 2017 geomagnetic storm. We investigated the contribution of the different species (ions and electrons) to the magnetic field deformation observed at ground magnetic stations (09°–45° MLat) using RAM-SCB simulations. The results show that the ions are the major contributor with ∼88% and electrons contribute ∼12% to the total ring current pressure. It is also found that the electron contribution is non-negligible (∼18%) to the ring current in dawn-side during the main phase of the storm. Thus, the electron contribution to the storm time ring current is important and should not be neglected.

DOI： 10.1029/2021ja029109

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JA029109

Magnetic Conjugacy of Pc1 Waves and Isolated Proton Precipitation at Subauroral Latitudes: Importance of Ionosphere as Intensity Modulation Region 査読有り Open Access

Ozaki M., Shiokawa K., Horne R.B., Engebretson M.J., Lessard M., Ogawa Y., Hosokawa K., Nosé M., Ebihara Y., Kadokura A., Yagitani S., Miyoshi Y., Hashimoto S., Sinha S., Sinha A.K., Seemala G.K., Jun C.W.

Geophysical Research Letters 48 巻 ( 5 ) 2021年3月

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

Pc1 geomagnetic pulsations, equivalent to electromagnetic ion cyclotron waves in the magnetosphere, display a specific amplitude modulation, though the region of the modulation remains an open issue. To classify whether the amplitude modulation has a magnetospheric or ionospheric origin, an isolated proton aurora (IPA), which is a proxy of Pc1 wave-particle interactions, is compared with the associated Pc1 waves for a geomagnetic conjugate pair, Halley Research Base in Antarctica and Nain in Canada. The temporal variation of an IPA shows a higher correlation coefficient (0.88) with Pc1 waves in the same hemisphere than that in the opposite hemisphere. This conjugate observation reveals that the classic cyclotron resonance is insufficient to determine the amplitude modulation. We suggest that direct wave radiation from the ionospheric current by IPA should also contribute to the amplitude modulation.

DOI： 10.1029/2020gl091384

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GL091384

Active auroral arc powered by accelerated electrons from very high altitudes. Open Access

Imajo S, Miyoshi Y, Kazama Y, Asamura K, Shinohara I, Shiokawa K, Kasahara Y, Kasaba Y, Matsuoka A, Wang SY, Tam SWY, Chang TF, Wang BJ, Angelopoulos V, Jun CW, Shoji M, Nakamura S, Kitahara M, Teramoto M, Kurita S, Hori T

Scientific reports 11 巻 ( 1 ) 頁： 1610 2021年1月

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

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 ~ 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 kilometres1. 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

その他リンク： http://www.nature.com/articles/s41598-020-79665-5

Pitch-Angle Scattering of Inner Magnetospheric Electrons Caused by ECH Waves Obtained With the Arase Satellite 査読有り

Fukizawa M., Sakanoi T., Miyoshi Y., Kazama Y., Katoh Y., Kasahara Y., Matsuda S., Matsuoka A., Kurita S., Shoji M., Teramoto M., Imajo S., Sinohara I., Wang S.Y., Tam S.W.Y., Chang T.F., Wang B.J., Jun C.W.

Geophysical Research Letters 47 巻 ( 23 ) 2020年10月

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

Electrostatic electron cyclotron harmonic (ECH) waves are generally excited in the magnetic equator region, in the sector from nightside to dayside during geomagnetically active conditions, and cause the pitch angle scattering by cyclotron resonance. The scattered electrons precipitate into the Earth's atmosphere and cause auroral emission. However, there is no observational evidence that ECH waves actually scatter electrons into the loss cone in the magnetosphere. In this study, from simultaneous wave and particle observation data obtained by the Arase satellite equipped with a high-pitch angular resolution electron analyzer, we present evidence that the ECH wave intensity near the magnetic equator is correlated with an electron flux inside the loss cone with an energy of about 5 keV. The simulation suggests that this electron flux contributes to the auroral emission at 557.7 nm with an intensity of about 200 R.

DOI： 10.1029/2020GL089926

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GL089926

The Modulation of Plasma and Waves by Background Electron Density Irregularities in the Inner Magnetosphere 査読有り

Yue C., Ma Q., Jun C.W., Bortnik J., Zong Q., Zhou X., Jang E., Reeves G.D., Spence H.E., Wygant J.R.

Geophysical Research Letters 47 巻 ( 15 ) 2020年8月

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

The background cold electron density plays an important role in plasma and wave dynamics. Here, we investigate an event with clear modulation of the particle fluxes and wave intensities by background electron density irregularities based on Van Allen Probes observations. The energies at the peak fluxes of protons and Helium ions of 100 eV to several keV are well correlated with the total electron density variation. Intense electromagnetic ion cyclotron (EMIC) and magnetosonic (MS) waves are simultaneously observed in the high-density regions and disappear in low-density regions. Based on the linear theory of wave growth, the EMIC waves are generated by the ~10 keV protons, while most MS waves are generated by the positive gradient of proton phase space density at several hundred eV in the high-density regions. Our results indicate the importance of background plasma density structures in generation of plasma waves by unstable ion distributions.

DOI： 10.1029/2020GL088855

Comprehensive Observations of Substorm-Enhanced Plasmaspheric Hiss Generation, Propagation, and Dissipation 査読有り

Liu N., Su Z., Gao Z., Zheng H., Wang Y., Wang S., Miyoshi Y., Shinohara I., Kasahara Y., Tsuchiya F., Kumamoto A., Matsuda S., Shoji M., Mitani T., Takashima T., Kazama Y., Wang B.J., Wang S.Y., Jun C.W., Chang T.F., Tam S.W.Y., Kasahara S., Yokota S., Keika K., Hori T., Matsuoka A.

Geophysical Research Letters 47 巻 ( 2 ) 2020年1月

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

Plasmaspheric hiss is an important whistler-mode emission shaping the Van Allen radiation belt environment. How the plasmaspheric hiss waves are generated, propagate, and dissipate remains under intense debate. With the five spacecraft of Van Allen Probes, Exploration of energization and Radiation in Geospace (Arase), and Geostationary Operational Environmental Satellites missions at widely spaced locations, we present here the first comprehensive observations of hiss waves growing from the substorm-injected electron instability, spreading within the plasmasphere, and dissipating over a large spatial scale. During substorms, hot electrons were injected energy-dispersively into the plasmasphere near the dawnside and, probably through a combination of linear and nonlinear cyclotron resonances, generated whistler-mode waves with globally drifting frequencies. These waves were able to propagate from the dawnside to the noonside, with the frequency-drifting feature retained. Approximately 5 hr of magnetic local time away from the source region in the dayside sector, the wave power was dissipated to (Formula presented.) of its original level.

DOI： 10.1029/2019GL086040

The Relationship Between EMIC Wave Properties and Proton Distributions Based on Van Allen Probes Observations 査読有り

Chao Yue, Chae‐Woo Jun, Jacob Bortnik, Xin An, Qianli Ma, Geoffrey D. Reeves, Harlan E. Spence, Andrew J. Gerrard, Matina Gkioulidou, Donald G. Mitchell, Craig A. Kletzing

Geophysical Research Letters 46 巻 ( 8 ) 頁： 4070 - 4078 2019年4月

Discovery of 1 Hz Range Modulation of Isolated Proton Aurora at Subauroral Latitudes 査読有り Open Access

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

Geophysical Research Letters 45 巻 ( 3 ) 頁： 1209 - 1217 2018年2月

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

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.

DOI： 10.1002/2017GL076486

Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes 査読有り Open Access

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

Geophysical Research Letters 43 巻 ( 15 ) 頁： 7859 - 7866 2016年8月

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

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 (1/8 s) images of proton-induced N2+ 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 100 s 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 100 s 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

Study of Pc1 pearl structures observed at multi-point ground stations in Russia, Japan, and Canada 査読有り

Jun C., Shiokawa K., Connors M., Schofield I., Poddelsky I., Shevtsov B.

Earth, Planets and Space 66 巻 ( 1 ) 2014年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth, Planets and Space

We investigate possible generation mechanisms of Pc1 pearl structures using multi-point induction magnetometers in Athabasca in Canada, Magadan in Russia, and Moshiri in Japan. We selected two Pc1 pulsations that were simultaneously observed at the three stations and applied a polarization analysis. In case 1, on 8 April 2010, Pc1 pearl structures were slightly different in some time intervals at different stations, and their polarization angles varied depending on the frequencies at the three stations. Case 2, on 11 April 2010, showed Pc1 pearl structures that were similar at different stations, and their polarization angle was independent of frequency at all three stations. In order to understand these differences, we performed two simple model calculations of Pc1 pearl structures under different conditions. The first model assumes that Pc1 waves propagated from a latitudinally extended source with different frequencies at different latitudes to the observation points, representing beating of these waves in the ionosphere. The second model considers Pc1 waves for which different frequencies are mixed at a point source to cause the beating at the source point, indicating that the Pc1 pearl structures are generated in the magnetosphere. The first model shows slightly different waveforms at different stations. In contrast, the second model shows identical waveforms at different stations. From these results, we conclude that, in case 1, Pc1 pearl structures were caused by beating in the ionosphere. On the other hand, in case 2, they were the result of magnetospheric effects. We suggest that beating processes in the ionosphere could be one of the generation mechanisms of Pc1 pearl structures.

DOI： 10.1186/s40623-014-0140-8

その他リンク： http://link.springer.com/content/pdf/10.1186/s40623-014-0140-8.pdf

Low-latitude Pi2 pulsations during intervals of quiet geomagnetic conditions (K<inf>p</inf>≤1) 査読有り Open Access

Kwon H.J., Kim K.H., Jun C.W., Takahashi K., Lee D.H., Lee E., Jin H., Seon J., Park Y.D., Hwang J.

Journal of Geophysical Research: Space Physics 118 巻 ( 10 ) 頁： 6145 - 6153 2013年10月

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

It has been reported that Pi2 pulsations can be excited under extremely quiet geomagnetic conditions (Kp=0). However, there have been few comprehensive reports of Pi2 pulsations in such a near ground state magnetosphere. To understand the characteristics of quiet-time Pi2 pulsations, we statistically examined Pi2 events observed on the nightside between 1800 and 0600 local time at the low-latitude Bohyun (BOH, L = 1.35) station in South Korea. We chose year 2008 for analysis because geomagnetic activity was unusually low in that year. A total of 982 Pi2 events were identified when Kp≤1. About 80% of the Pi2 pulsations had a period between 110 and 300 s, which significantly differs from the conventional Pi2 period from 40 to 150 s. Comparing Pi2 periods and solar wind conditions, we found that Pi2 periods decrease with increasing solar wind speed, consistent with the result of Troitskaya (1967). The observed wave properties are discussed in terms of plasmaspheric resonance, which has been proposed for Pi2 pulsations in the inner magnetosphere. We also found that Pi2 pulsations occur quasi-periodically with a repetition period of ∼23-38 min. We will discuss what determines such a recurrence time of Pi2 pulsations under quiet geomagnetic conditions. Key Points Pi2 pulsations during quiet geomagnetic conditions Pi2 frequencies depending on solar wind speeds Quasi-periodic Pi2 pulsations with an occurrence rate of about 23-53 min ©2013. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/jgra.50582

Statistical Analysis of Low-latitude Pi2 Pulsations Observed at Bohyun Station in Korea 査読有り

Chae-Woo Jun, Khan-Huk Kim, Hyuck-Jin Kwon, Dong-Hun Lee, Ensang Lee, Young-Deuk Park, Junga Hwang

Journal of Astronomy and Space Sciences 30 巻 ( 1 ) 頁： 25 - 32 2013年3月

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