Yoshiya Kasahara

Kanazawa University

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Co-Authors

Yoshizumi Miyoshi

Nagoya University

135

Ayako Matsuoka

Institute of Space and Astronautical Science

116

Iku Shinohara

Japan Aerospace Exploration Agency

106

Atsushi Kumamoto

Tohoku University

102

Shoya Matsuda

Kanazawa University

Fuminori Tsuchiya

Tohoku University

Masafumi Shoji

Nagoya University

Yasumasa Kasaba

Tohoku University

Tomoaki Hori

Nagoya University

Shoichiro Yokota

Osaka University

Cooperative Institutions

Nagoya University

125

John Wiley & Sons (United States)

124

Charles River Laboratories (Netherlands)

123

Kyoto University

Goddard Space Flight Center

Tohoku University

Institute of Space and Astronautical Science

Japan Aerospace Exploration Agency

Planetary Science Institute

The University of Tokyo

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Variation in crossover frequency of EMIC waves in plasmasphere estimated from ion cyclotron whistler waves observed by Van Allen Probe A

Geophysical Research Letters (2016)

Shoya Matsuda Yoshiya Kasahara C. Kletzing

Abstract We report variations in the propagation of the H + band ion cyclotron whistlers observed by Van Allen Probe A. Ion cyclotron whistlers are one of the EMIC (electromagnetic ion cyclotron) waves generated by mode conversion from lightning whistlers. Crossover frequency is an important frequency for the ion cyclotron whistlers, which is a function of the variations in the local heavy‐ion composition. We surveyed waveform data obtained by the Electric and Magnetic Field Instrument and Integrated Science instrument and found that 3461 H + band ion cyclotron whistlers were observed from 572 km to 5992 km in altitude. The main finding is that the crossover frequencies of the observed events decreased with increasing altitude. These results support the hypothesis that the total heavy‐ion density decreases with increasing altitude. Furthermore, in 96% of all observed events, the crossover frequencies exceeded , which suggests that the EMIC dispersion relation contains a frequency gap of around .

Whistler

Plasmasphere

10.1002/2015gl066893

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Citations (7)

Propagation Mechanism of Medium Wave Broadcasting Waves Observed by the Arase Satellite: Hectometric Line Spectra

Journal of Geophysical Research Space Physics (2021)

K. Hashimoto Atsuki Shinbori Y. Otsuka Fuminori Tsuchiya Atsushi Kumamoto

Abstract A new type of terrestrial line spectra found by the Arase satellite was reported in 2018. These spectra are called “hectometric line spectra (HLS)”. They primarily consist of constant frequency narrowband components at frequencies between 525 kHz and 1,700 kHz, which originate and are sometimes amplified from AM broadcasting waves. In addition to these, other generated emissions are observed. Entrances and the mode conversion of the AM broadcasting waves into the equatorial and low‐latitude ionosphere with plasma density depletion called plasma bubbles are observed. Electron density profiles and equatorial plasma bubbles are examined through Global Positioning System (GPS)‐Total electron content (TEC) analyses. As a result, the Arase satellite which observed the HLS passed through the TEC depression region near the equatorial ionosphere associated with plasma bubbles. The scenario based on the mode conversion of the L‐O mode to the Z mode and vice versa was confirmed with observations and GPS‐TEC analyses. Another entrance when f o F 2 estimated from TEC is lower than 1,000 kHz instead of a plasma bubble is also found. No mode conversion is necessary, then.

Narrowband

10.1029/2021ja029813

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Citations (3)

Energetic Electron Precipitation Associated With Pulsating Aurora Observed by VLF Radio Propagation During the Recovery Phase of a Substorm on 27 March 2017

Geophysical Research Letters (2018)

Fuminori Tsuchiya A. Hirai T. Obara Hiroaki Misawa Satoshi Kurita

Abstract Recent studies suggest that electrons with energies up to several hundred keV precipitate into the atmosphere associated with pulsating aurora (PsA). It is debated the highest energy of precipitating electrons associated with PsA. Here we report for the first time that the energy extends to relativistic energies. PsA was observed by THEMIS all‐sky imagers during a substorm that occurred on 27 March 2017. Energetic electron precipitation was detected by very low frequency subionospheric propagation. We found similar time variations between the auroral intensity and perturbation of the received radio signal intensity when the PsA occurred on the radio path. The perturbation showed a short recovery time of ~2 s. The recovery time indicates relaxation from ionospheric modification due to energetic electron precipitation and depends on the stopping altitude of the electrons. The recovery time required a stopping altitude of 50–60 km and indicates that the PsA is accompanied by relativistic electron precipitation.

Substorm

Electron precipitation

Microburst

10.1029/2018gl080222

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Citations (9)

EMIC Waves Converted From Equatorial Noise Due to M/Q = 2 Ions in the Plasmasphere: Observations From Van Allen Probes and Arase

Geophysical Research Letters (2019)

Yoshizumi Miyoshi Shoya Matsuda Satoshi Kurita K. Nomura K. Keika

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 ions is ~10% below 3,000 km. The quantitative estimation of the ion composition will contribute to improving the plasma model of the deep plasmasphere and the topside ionosphere.

Plasmasphere

Emic and etic

Van Allen Probes

10.1029/2019gl083024

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Citations (34)

Discovery of proton hill in the phase space during interactions between ions and electromagnetic ion cyclotron waves

Scientific Reports (2021)

Masafumi Shoji Yoshizumi Miyoshi L. M. Kistler Kazushi Asamura Ayako Matsuoka

Abstract A study using Arase data gives the first observational evidence that the frequency drift of electromagnetic ion cyclotron (EMIC) waves is caused by cyclotron trapping. EMIC emissions play an important role in planetary magnetospheres, causing scattering loss of radiation belt relativistic electrons and energetic protons. EMIC waves frequently show nonlinear signatures that include frequency drift and amplitude enhancements. While nonlinear growth theory has suggested that the frequency change is caused by nonlinear resonant currents owing to cyclotron trapping of the particles, observational evidence for this has been elusive. We survey the wave data observed by Arase from March, 2017 to September 2019, and find the best falling tone emission event, one detected on 11th November, 2017, for the wave particle interaction analysis. Here, we show for the first time direct evidence of the formation of a proton hill in phase space indicating cyclotron trapping. The associated resonance currents and the wave growth of a falling tone EMIC wave are observed coincident with the hill, as theoretically predicted.

Cyclotron resonance

Ion cyclotron resonance

10.1038/s41598-021-92541-0

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Citations (17)

Akebono observations of EMIC waves in the slot region of the radiation belts

Geophysical Research Letters (2013)

K. Sakaguchi Yoshiya Kasahara Masafumi Shoji Yoshiharu Omura Yoshizumi Miyoshi

This paper describes a unique observation of electromagnetic ion cyclotron (EMIC) waves in the deep inner magnetosphere at L = 2.5 − 5 made by the Akebono satellite at altitudes of 3,300 − 8,700 km. The mode conversion, i.e., L mode (He + band) → R mode (He + band) → L mode (O + band) was clearly identified from the equator to high latitudes. In addition, we found rising tone structures, recently identified as EMIC triggered emissions, which could lead to bursty precipitation of relativistic electrons. First, we estimated the ion composition ratio (H + , He + , O + ) = (83%, 16%, 1%) from polarization analysis. Second, we estimated minimum resonant electron energies with the observed EMIC waves and triggered emissions to be ∼1–10 MeV. The satellite trajectory during the wave observation was primarily through the slot region of electron radiation belts. The collocation implies possible contribution of EMIC waves to formation of the slot region of radiation belts after a magnetic storm.

Van Allen Probes

Emic and etic

Electron precipitation

10.1002/2013gl058258

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Citations (54)

A Statistical Study of the Solar Wind Dependence of Multi‐Harmonic Toroidal ULF Waves Observed by the Arase Satellite

Journal of Geophysical Research Space Physics (2021)

Kazuhiro Yamamoto K. Seki Ayako Matsuoka Shun Imajo M. Teramoto

Abstract Toroidal standing Alfvén wave is one of the ultra‐low frequency waves that are frequently observed in the terrestrial magnetosphere. They sometimes exhibit multi‐harmonic frequency spectra, indicating wide energy range input in the magnetosphere. However, their energy source has not been fully understood due to the lack of statistical studies. Here we used the data of the Arase satellite observations for ∼3.5 years and conducted a statistical analysis of the solar wind dependence of the occurrence rate, wave power, and frequency of the multi‐harmonic toroidal waves. We automatically detected the multi‐harmonic waves and categorized them into four groups according to the solar wind velocity and the cone angle of the interplanetary magnetic field. We found that the occurrence rate and wave power of the multi‐harmonic waves increase with the solar wind velocity on the flank sides. In the noon sector, the occurrence rate of the multi‐harmonic waves increases with the decrease of the cone angle. The median frequency of the multi‐harmonic waves on the dayside is positively correlated with the upstream wave frequency predicted by the theory of the ion beam instability for a small cone angle. The occurrence rate also increases with the solar wind dynamic pressure fluctuations. Therefore, we suggest that the Kelvin‐Helmholtz instability, the upstream waves, and the dynamic pressure fluctuations are possible sources of the multi‐harmonic waves. This study sheds light on the activity of the multi‐harmonic waves which can affect radiation belt electrons under various solar wind conditions.

Harmonic

Infragravity wave

Noon

10.1029/2021ja029840

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Citations (9)

Issue Information

Geophysical Research Letters (2018)

Noah S. Diffenbaugh Suzana J. Camargo Mónica Cárdenas R. Carey Rose M. Cory

No abstract is available for this article.

10.1002/grl.56391

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Citations (0)

Global Maps of Solar Wind Electron Modification by Electrostatic Waves Above the Lunar Day Side: Kaguya Observations

Geophysical Research Letters (2021)

Yuki Harada Yoshiya Kasahara Masaki N. Nishino Satoshi Kurita Y. Saito

Abstract The Moon drives observable perturbations in the upstream solar wind in a similar manner to the terrestrial foreshock. Recent observations suggested that lunar dayside electrostatic waves can arise from two different driving mechanisms, both involving reflected particles from lunar crustal magnetic fields. However, their association with the global distribution of lunar magnetic anomalies have not been fully characterized. Here we exploit polar orbiting Kaguya to generate first global maps of electrostatic waves and solar wind electron modification above the day side of the Moon. The maps clearly demonstrate that the two signatures are correlated with lunar crustal magnetic fields. Additionally, we observe different characteristics of electron modification for different interplanetary magnetic field orientations. The lunar crustal magnetic fields cause a wide range of reflected electron and ion intensities, thereby serving as a test bed to investigate the relative roles of reflected particles on wave excitation and particle heating.

10.1029/2021gl095260

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Citations (3)

Pulsating aurora from electron scattering by chorus waves

Nature (2018)

Satoshi Kasahara Yoshizumi Miyoshi Shoichiro Yokota Takefumi Mitani Yoshiya Kasahara

Electron precipitation

Chorus

Substorm

Plasma sheet

Van Allen Probes

10.1038/nature25505

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Citations (200)