研究者詳細 - JUN Chae-Woo

論文 - JUN Chae-Woo

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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

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