Spatial Distribution of Fine‐Structured and Unstructured EMIC Waves Observed by the Arase Satellite

Matsuda, Shoya; Kasahara, Yoshiya; Miyoshi, Yoshizumi; Nomura, Reiko; Motomizu, Shoji; Matsuoka, A.; Kasaba, Yasumasa; Kurita, Satoshi; Teramoto, Masaaki; Ishisaka, Keigo

doi:10.1029/2018gl080109

Cited by 20 publications

(28 citation statements)

References 37 publications

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“…6 .) This frequency characteristic is similar to that of propagating EMIC waves observed at L = 2–5 by the Akebono (Sakaguchi et al 2013 ) and Arase (Matsuda et al 2018b ) satellites. However, we do not further focus on them, because they have much smaller wave power than the waves mentioned above (the B w⊥ waves around 02:40–02:50 UT and 07:10–07:50 UT), they only appear for a short time, and they seem to show no clear values of θ Bk and ε (i.e., degree of polarization less than 0.8).…”

Section: Simultaneous Observations By Van Allen Probe B and Arase On supporting

confidence: 80%

Oxygen torus and its coincidence with EMIC wave in the deep inner magnetosphere: Van Allen Probe B and Arase observations

Nosé

Matsuoka

Kumamoto

et al. 2020

Earth Planets Space

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We investigate the longitudinal structure of the oxygen torus in the inner magnetosphere for a specific event found on 12 September 2017, using simultaneous observations from the Van Allen Probe B and Arase satellites. It is found that Probe B observed a clear enhancement in the average plasma mass (M) up to 3–4 amu at L = 3.3–3.6 and magnetic local time (MLT) = 9.0 h. In the afternoon sector at MLT ~ 16.0 h, both Probe B and Arase found no clear enhancements in M. This result suggests that the oxygen torus does not extend over all MLT but is skewed toward the dawn. Since a similar result has been reported for another event of the oxygen torus in a previous study, a crescent-shaped torus or a pinched torus centered around dawn may be a general feature of the O+ density enhancement in the inner magnetosphere. We newly find that an electromagnetic ion cyclotron (EMIC) wave in the H+ band appeared coincidently with the oxygen torus. From the lower cutoff frequency of the EMIC wave, the ion composition of the oxygen torus is estimated to be 80.6% H+, 3.4% He+, and 16.0% O+. According to the linearized dispersion relation for EMIC waves, both He+ and O+ ions inhibit EMIC wave growth and the stabilizing effect is stronger for He+ than O+. Therefore, when the H+ fraction or M is constant, the denser O+ ions are naturally accompanied by the more tenuous He+ ions, resulting in a weaker stabilizing effect (i.e., larger growth rate). From the Probe B observations, we find that the growth rate becomes larger in the oxygen torus than in the adjacent regions in the plasma trough and the plasmasphere.

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Section: Simultaneous Observations By Van Allen Probe B and Arase On supporting

confidence: 80%

Oxygen torus and its coincidence with EMIC wave in the deep inner magnetosphere: Van Allen Probe B and Arase observations

Nosé

Matsuoka

Kumamoto

et al. 2020

Earth Planets Space

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“…The ambient magnetic field is observed by the Magnetic Field Experiment (MGF) on board the Arase satellite (Matsuoka et al, ). Typical EMIC waves observed by Arase are reported in Matsuda et al () and Shoji et al ().…”

Section: Analysis Of Van Allen Probe and Arase Observationsmentioning

confidence: 62%

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

Miyoshi

Matsuda

Kurita

et al. 2019

Geophysical Research Letters

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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.

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“…For example, the minimum energy of precipitating electrons driven by EMIC waves is still under debate and the improved resolution in energy and pitch angle from new CubeSats will potentially provide insightful observational evidence. It would also be interesting to understand if the recently identified latitudinal dependence of fine‐structured EMIC waves (Matsuda et al, ) drives different patterns of particle precipitation. These interesting investigations are beyond the scope of the present study, and thus left as future work.…”

Section: Summary and Discussionmentioning

confidence: 99%

Energetic Electron Precipitation: Multievent Analysis of Its Spatial Extent During EMIC Wave Activity

Capannolo

et al. 2019

JGR Space Physics

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Electromagnetic ion cyclotron (EMIC) waves can drive precipitation of tens of keV protons and relativistic electrons, and are a potential candidate for causing radiation belt flux dropouts. In this study, we quantitatively analyze three cases of EMIC-driven precipitation, which occurred near the dusk sector observed by multiple Low-Earth-Orbiting (LEO) Polar Operational Environmental Satellites/Meteorological Operational satellite programme (POES/MetOp) satellites. During EMIC wave activity, the proton precipitation occurred from few tens of keV up to hundreds of keV, while the electron precipitation was mainly at relativistic energies. We compare observations of electron precipitation with calculations using quasi-linear theory. For all cases, we consider the effects of other magnetospheric waves observed simultaneously with EMIC waves, namely, plasmaspheric hiss and magnetosonic waves, and find that the electron precipitation at MeV energies was predominantly caused by EMIC-driven pitch angle scattering. Interestingly, each precipitation event observed by a LEO satellite extended over a limited L shell region (ΔL~0.3 on average), suggesting that the pitch angle scattering caused by EMIC waves occurs only when favorable conditions are met, likely in a localized region. Furthermore, we take advantage of the LEO constellation to explore the occurrence of precipitation at different L shells and magnetic local time sectors, simultaneously with EMIC wave observations near the equator (detected by Van Allen Probes) or at the ground (measured by magnetometers). Our analysis shows that although EMIC waves drove precipitation only in a narrow ΔL, electron precipitation was triggered at various locations as identified by POES/MetOp over a rather broad region (up to~4.4 hr MLT and~1.4 L shells) with similar patterns between satellites.

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Spatial Distribution of Fine‐Structured and Unstructured EMIC Waves Observed by the Arase Satellite

Cited by 20 publications

References 37 publications

Oxygen torus and its coincidence with EMIC wave in the deep inner magnetosphere: Van Allen Probe B and Arase observations

Oxygen torus and its coincidence with EMIC wave in the deep inner magnetosphere: Van Allen Probe B and Arase observations

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

Energetic Electron Precipitation: Multievent Analysis of Its Spatial Extent During EMIC Wave Activity

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