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

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