Drift‐Bounce Resonance Between Pc5 Pulsations and Ions at Multiple Energies in the Nightside Magnetosphere: Arase and MMS Observations

• Published in: Geophysical research letters 2018-08, Vol.45 (15), p.7277-7286
• Main Authors: Oimatsu, S., Nosé, M., Teramoto, M., Yamamoto, K., Matsuoka, A., Kasahara, S., Yokota, S., Keika, K., Le, G., Nomura, R., Fujimoto, A., Sormakov, D., Troshichev, O., Tanaka, Y.‐M., Shinohara, M., Shinohara, I., Miyoshi, Y., Slavin, J. A., Ergun, R. E., Lindqvist, P.‐A.
• Format: Article
• Language: English
• Subjects: Acceleration; Activation; Charged particles; Drift; Exploration; Fluctuations; Geomagnetic pulsations; Geomagnetism; Hydrogen; Ion flux; Ion fluxes; Ions; Magnetic resonance; Magnetic storms; Magnetism; Magnetosphere; Magnetospheres; Magnetospheric-solar wind relationships; Oscillations; Pc5 waves; Plasma instabilities; Radiation; Remote sensing; Resonance; Satellite observation; Satellites; Solar wind; Spaceborne remote sensing; Storms; Wave number; Wave propagation; Wavelengths
• ISSN: 0094-8276; 1944-8007; 1944-8007
• DOI: 10.1029/2018GL078961

A Pc5 wave is observed by the Exploration of energization and Radiation in Geospace Arase satellite in the inner magnetosphere (L ~5.4–6.1) near postmidnight (L‐magnetic local time ~1.8–2.5 hr) during the storm recovery phase on 27 March 2017. Its azimuthal wave number (m‐number) is estimated using two independent methods with satellites and ground observations to be −8 to −15. The direct measurement of the m‐number enables us to calculate the resonance energy. The flux oscillations of H+ and O+ ions at ≥ 56.3 keV are caused by drift resonance and those of O+ ions at ≤ 18.6 keV by bounce resonance. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. The enhancement of the O+/H+ flux ratio at ≤ 18.6 keV indicates selective acceleration of O+ ions through bounce resonance. Plain Language Summary Geomagnetic pulsations are magnetic fluctuations excited by solar wind or plasma instabilities in the magnetosphere. Pc5 waves are continuous geomagnetic pulsations with a period of 150–600 s. A Pc5 wave was observed in the inner magnetosphere during a magnetic storm on 27 March 2017. It propagated westward with a wave number of 8 to 15 and resonated with charged particles, resulting in oscillations of the H+ and O+ ion fluxes at ≥ 56.3 keV and the O+ ion fluxes at ≤ 18.6 keV. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. At the same time, the O+/H+ flux ratio at ≤ 18.6 keV enhanced corresponding to the O+ ion flux oscillations, which indicates selective acceleration of O+ ions through resonances. Key Points A large‐amplitude Pc5 wave is observed by Arase and MMS1 in the postmidnight region at L > 5.4 during the storm recovery phase We estimate the m‐number of the Pc5 wave to be −8 to −15 by using two independent methods with satellites and ground observations We simultaneously observe the drift resonance for H+ and O+ ions at ≥ 56.3 keV and bounce resonance for O+ ions at ≤ 18.6 keV