Biblio

Found 10 results
Filters: Author is Miyoshi, Y.  [Clear All Filters]
2019
Authors: Miyoshi Y, Matsuda S., Kurita S., Nomura K., Keika K, et al.
Title: EMIC waves converted from equatorial noise due to M/Q=2 ions in the plasmasphere: Observations from Van Allen Probes and Arase
Abstract: Equatorial noise (EN) emissions are observed inside and outside the plasmapause. EN emissions are referred to as magnetosonic mode waves. Using data from Van Allen Probes and Arase, we found conversion from EN emissions to electromagnetic ion cyclotron (EMIC) waves in the plasmasphere and in the topside ionosphere. A low frequency part of EN emissions becomes EMIC waves through branch splitting of EN emissions, and the mode conversion from EN to EMIC waves occurs around the frequency of M/Q=2 (deuteron and/or alpha particles) cyclotron frequency. These processes result in plasmaspheric EMIC waves. We investigated the ion composition ratio by characteristic frequencies of EN emissions and EMIC waves and obtained ion composition ratios. We found that the maximum composition ratio of M/Q=2 io. . .
Date: 04/2019 Publisher: Geophysical Research Letters DOI: 10.1029/2019GL083024 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL083024
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2018
Authors: é M., Matsuoka A., Kumamoto A., Kasahara Y., Goldstein J, et al.
Title: Longitudinal Structure of Oxygen Torus in the Inner Magnetosphere: Simultaneous Observations by Arase and Van Allen Probe A
Abstract: Simultaneous observations of the magnetic field and plasma waves made by the Arase and Van Allen Probe A satellites at different magnetic local time (MLT) enable us to deduce the longitudinal structure of an oxygen torus for the first time. During 04:00–07:10 UT on 24 April 2017, Arase flew from L = 6.2 to 2.0 in the morning sector and detected an enhancement of the average plasma mass up to ~3.5 amu around L = 4.9–5.2 and MLT = 5.0 hr, implying that the plasma consists of approximately 15% O+ ions. Probe A moved outbound from L = 2.0 to 6.2 in the afternoon sector during 04:10–07:30 UT and observed no clear enhancements in the average plasma mass. For this event, the O+ density enhancement in the inner magnetosphere (i.e., oxygen torus) does not extend over all MLT but is skewed tow. . .
Date: 10/2018 Publisher: Geophysical Research Letters Pages: 10,177 - 10,184 DOI: 10.1029/2018GL080122 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL080122
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Authors: Kurita S., Miyoshi Y, Shiokawa K., Higashio N., Mitani T., et al.
Title: Rapid loss of relativistic electrons by EMIC waves in the outer radiation belt observed by Arase, Van Allen Probes, and the PWING ground stations
Abstract: There has been increasing evidence for pitch angle scattering of relativistic electrons by electromagnetic ion cyclotron (EMIC) waves. Theoretical studies have predicted that the loss time scale of MeV electrons by EMIC waves can be very fast, suggesting that MeV electron fluxes rapidly decrease in association with the EMIC wave activity. This study reports on a unique event of MeV electron loss induced by EMIC waves based on Arase, Van Allen Probes, and ground‐based network observations. Arase observed a signature of MeV electron loss by EMIC waves, and the satellite and ground‐based observations constrained spatial‐temporal variations of the EMIC wave activity during the loss event. Multi‐satellite observation of MeV electron fluxes showed that ~2.5 MeV electron fluxes substantia. . .
Date: 11/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL080262 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL080262
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2017
Authors: Oyama S., Kero A., Rodger C. J., Clilverd M A, Miyoshi Y, et al.
Title: Energetic electron precipitation and auroral morphology at the substorm recovery phase
Abstract: It is well known that auroral patterns at the substorm recovery phase are characterized by diffuse or patch structures with intensity pulsation. According to satellite measurements and simulation studies, the precipitating electrons associated with these aurorae can reach or exceed energies of a few hundreds of keV through resonant wave-particle interactions in the magnetosphere. However, because of difficulty of simultaneous measurements, the dependency of energetic electron precipitation (EEP) on auroral morphological changes in the mesoscale has not been investigated to date. In order to study this dependency, we have analyzed data from the European Incoherent Scatter (EISCAT) radar, the Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) riometer, collocated cameras, ground-based m. . .
Date: 05/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023484 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023484/full
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Authors: Ren Jie, Zong Q. G., Miyoshi Y, Zhou X. Z., Wang Y. F., et al.
Title: Low-energy (< 200 eV) electron acceleration by ULF waves in the plasmaspheric boundary layer: Van Allen Probes observation
Abstract: We report observational evidence of cold plamsmaspheric electron (< 200 eV) acceleration by ultra-low-frequency (ULF) waves in the plasmaspheric boundary layer on 10 September 2015. Strongly enhanced cold electron fluxes in the energy spectrogram were observed along with second harmonic mode waves with a period of about 1 minute which lasted several hours during two consecutive Van Allen Probe B orbits. Cold electron (<200 eV) and energetic proton (10-20 keV) bi-directional pitch angle signatures observed during the event are suggestive of the drift-bounce resonance mechanism. The correlation between enhanced energy fluxes and ULF waves leads to the conclusions that plasmaspheric dynamics is strongly affected by ULF waves. Van Allen Probe A and B, GOES 13, GOES 15 and MMS 1 observations su. . .
Date: 08/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024316 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024316/full
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2016
Authors: Ozaki M., Shiokawa K., Miyoshi Y, Kataoka R., Yagitani S., et al.
Title: Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes
Abstract: 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 sec. . .
Date: 08/2016 Publisher: Geophysical Research Letters Pages: 7859 - 7866 DOI: 10.1002/2016GL070008 Available at: http://doi.wiley.com/10.1002/2016GL070008
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Authors: Nomura R., Shiokawa K., Omura Y., Ebihara Y., Miyoshi Y, et al.
Title: Pulsating proton aurora caused by rising tone Pc1 waves
Abstract: We found rising tone emissions with a dispersion of ∼1 Hz per several tens of seconds in the dynamic spectrum of a Pc1 geomagnetic pulsation (Pc1) observed on the ground. These Pc1 rising tones were successively observed over ∼30 min from 0250 UT on 14 October 2006 by an induction magnetometer at Athabasca, Canada (54.7°N, 246.7°E, magnetic latitude 61.7°N). Simultaneously, a Time History of Events and Macroscale Interactions during Substorms panchromatic (THEMIS) all-sky camera detected pulsations of an isolated proton aurora with a period of several tens of seconds, ∼10% variations in intensity, and fine structures of 3° in magnetic longitudes. The pulsations of the proton aurora close to the zenith of ATH have one-to-one correspondences with the Pc1 rising tones. This suggests. . .
Date: 02/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: n/a - n/a DOI: 10.1002/2015JA021681 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2015JA021681/full
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2015
Authors: Miyoshi Y, Oyama S., Saito S., Kurita S., Fujiwara H., et al.
Title: Energetic electron precipitation associated with pulsating aurora: EISCAT and Van Allen Probe observations
Abstract: Pulsating auroras show quasi-periodic intensity modulations caused by the precipitation of energetic electrons of the order of tens of keV. It is expected theoretically that not only these electrons but also sub-relativistic/relativistic electrons precipitate simultaneously into the ionosphere owing to whistler-mode wave–particle interactions. The height-resolved electron density profile was observed with the European Incoherent Scatter (EISCAT) Tromsø VHF radar on 17 November 2012. Electron density enhancements were clearly identified at altitudes >68 km in association with the pulsating aurora, suggesting precipitation of electrons with a broadband energy range from ~10 keV up to at least 200 keV. The riometer and network of subionospheric radio wave observations also showed the energ. . .
Date: 03/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020690 Available at: http://doi.wiley.com/10.1002/2014JA020690
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2009
Authors: Ohtani S, Miyoshi Y, Singer H J, and Weygand J M
Title: On the loss of relativistic electrons at geosynchronous altitude: Its dependence on magnetic configurations and external conditions
Abstract: [1] The present study statistically examines geosynchronous magnetic configurations and external conditions that characterize the loss of geosynchronous MeV electrons. The loss of MeV electrons often takes place during magnetospheric storms, but it also takes place without any clear storm activity. It is found that irrespective of storm activity, the day-night asymmetry of the geosynchronous H (north-south) magnetic component is pronounced during electron loss events. For the loss process, the magnitude, rather than the duration, of the magnetic distortion appears to be important, and its effective duration can be as short as ∼30 min. The solar wind dynamic pressure tends to be high and interplanetary magnetic field BZ tends to be southward during electron loss events. Under such externa. . .
Date: 01/2009 Publisher: Journal of Geophysical Research DOI: 10.1029/2008JA013391 Available at: http://onlinelibrary.wiley.com/doi/10.1029/2008JA013391/full
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2008
Authors: Jordanova V K, Albert J, and Miyoshi Y
Title: Relativistic electron precipitation by EMIC waves from self-consistent global simulations
Abstract: [1] We study the effect of electromagnetic ion cyclotron (EMIC) wave scattering on radiation belt electrons during the large geomagnetic storm of 21 October 2001 with minimum Dst = −187 nT. We use our global physics-based model, which solves the kinetic equation for relativistic electrons and H+, O+, and He+ ions as a function of radial distance in the equatorial plane, magnetic local time, energy, and pitch angle. The model includes time-dependent convective transport and radial diffusion and all major loss processes and is coupled with a dynamic plasmasphere model. We calculate the excitation of EMIC waves self-consistently with the evolving plasma populations. Particle interactions with these waves are evaluated according to quasi-linear theory, using diffusion coefficients for a mult. . .
Date: 03/2008 Publisher: Journal of Geophysical Research DOI: 10.1029/2008JA013239 Available at: http://onlinelibrary.wiley.com/doi/10.1029/2008JA013239/abstract
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