Giant Pulsations Excited by a Steep Earthward Gradient of Proton Phase Space Density: Arase Observation

Yamamoto, Kazuhiro; Nosé, M.; Kasahara, Satoshi; Yokota, Shoichiro; Keika, K.; Matsuoka, A.; Teramoto, Masaaki; Takahashi, Kazue; Oimatsu, S.; Nomura, Reiko; Vellante, M.; Heilig, B.; Fujimoto, Akiko; Tanaka, Yoshimasa; Shinohara, Masanao; Shinohara, I.; Miyoshi, Yoshizumi

doi:10.1029/2018gl078293

Cited by 11 publications

(17 citation statements)

References 39 publications

(71 reference statements)

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“…Southwood et al (1969) has proposed that poloidal mode waves are associated with the drift‐bounce resonance in a homogeneous field. Recently, Yamamoto et al (2018) observed the excitation of compressional pulsations propagating westward with the m number of m = − 50 around the magnetic equator. The waves were odd mode waves and in the drift resonance with energetic ions.…”

Section: Discussionmentioning

confidence: 99%

“…It is interesting to see that these wave properties are actually seen in the simulation as shown in Figure 3. Yamamoto et al (2018) consider that the Pc5 waves are mainly compressional because dB r of fundamental mode is small, and compressional mode becomes prominent around the magnetic equator (Takahashi et al, 1992). Since we show the global distribution of Pc5 waves at MLAT = 1° in Figure 3, this interpretation can qualitatively explain the excited Pc5 polarization.…”

Section: Discussionmentioning

confidence: 99%

“…There have been a number of observational studies discussing the drift‐bounce resonance excitation of internally driven ULF waves. While there have been several studies which observed fundamental poloidal waves associated with the drift resonance (e.g., Dai et al, 2013; Yamamoto et al, 2018), previous observations overwhelmed the drift‐bounce resonance excitation of second harmonic poloidal waves (e.g., Le et al, 2017; Min et al, 2017; Oimatsu et al, 2018; Takahashi et al, 1985, 2018; Yamamoto et al, 2019). These observations suggest that internally driven ULF waves excited by the drift‐bounce resonance tend to have a poloidal polarization and propagate westward with high m numbers (| m | ~ 70–200) (e.g., Dai et al, 2013; Takahashi et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Excitation of Internally Driven ULF Waves by the Drift‐Bounce Resonance With Ring Current Ions Based on the Drift‐Kinetic Simulation

et al. 2020

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We investigated the excitation mechanism and global distribution of internally driven Pc3-Pc5 ultralow-frequency waves in the inner magnetosphere using a kinetic and self-consistent simulation (Geospace Environment Modeling System for Integrated Studies-Ring Current model). These waves can be excited through the drift-bounce resonance with ring current ions injected into the inner magnetosphere during substorms. Initial phase space density of ring current ions is the butterfly-like distribution with the asymmetry in pitch angle direction. We find two kinds of internally driven ultralow-frequency waves. First, the dynamic power spectra of the field fluctuations show the excitation of poloidal, toroidal, and compressional Pc5 waves. We find that the excited waves are fundamental modes propagating westward with the azimuthal wave number of m~− 50. These waves are excited by the drift resonance with ions having the energy of 50-150 keV. Second, we can reproduce the excitation of poloidal Pc3 waves in the dusk region with m~− 30, which are driven by the bounce resonance with ions having energies of 20-50 keV for the first time. We investigate the energy transfer between ions and waves and find that poloidal Pc5 and Pc3 waves are excited mainly by positive energy gradient of the phase space density, while we find the inward gradient of the phase space density at L > 6. The velocity distribution of the growth rate suggests that Pc5 waves are driven by ions with pitch angle of around 90°, while Pc3 waves are excited by ions at oblique pitch angle.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Excitation of Internally Driven ULF Waves by the Drift‐Bounce Resonance With Ring Current Ions Based on the Drift‐Kinetic Simulation

et al. 2020

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“…These results indicate that this transverse Pc3-4 wave is not due to upstream waves. Instead, a possible explanation is the fundamental standing wave caused by the drift-bounce resonance (e.g., Dai et al 2013;Oimatsu et al 2018;Yamamoto et al 2018), although we do not further discuss this possibility, because it is beyond the scope of this study.…”

Section: Signatures Of Standing Alfvén Waves and Upper Hybrid Resonanmentioning

confidence: 99%

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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“…Pc4-5 toroidal waves with low m are usually considered to be caused by external sources, such as Kelvin-Helmholtz instability along the magnetopause (e.g., Claudepierre et al, 2008;Ling et al, 2018;Rae et al, 2005;Zhang et al, 2018), solar wind dynamic pressure impulse (e.g., Allan et al, 1986;Degeling et al, 2014;Lee & Lysak, 1989;Shen et al, 2015Shen et al, , 2017Shi et al, 2013Shi et al, , 2014Tian et al, 2016;Zong et al, 2012), and foreshock transients (e.g., Hartinger et al, 2013;Shen et al, 2018). Pc4-5 poloidal waves with high wave number are usually driven by localized kinetic plasma instabilities such as the drift-bounce resonance instability (e.g., Oimatsu et al, 2018;Southwood, 1976;Yang et al, 2010), the free energy could be generally provided by bump-on-tail distribution at low-energy (~1-10 keV; e.g., Liu et al, 2013;Shi et al, 2018;Takahashi et al, 2018) or inward gradient of ion phase space density (PSD) at high energy (tens to hundreds of keV; e.g., Dai et al, 2013;Min et al, 2017;Yamamoto et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Pc4‐5 Poloidal ULF Wave Observed in the Dawnside Plasmaspheric Plume

et al. 2019

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A localized Pc4-5 ultralow-frequency (ULF) wave event associated with a plasmaspheric plume was observed by THEMIS-E on the dawnside near L = 6, which was identified as a second harmonic poloidal wave. The plume was identified as a sudden density enhancement during an outbound pass. The charged particle populations in the plume have a variety of periodic modulation characteristics at different energies. First, there is an antiphase relationship between magnetic field Br and particle flux across a wide energy range both for ions and electrons (~50 keV to 1 MeV). Second, there is a 180°phase shift in the modulated ion flux within an energy range of~2-6 keV, with negative slope dispersions of ion pitch angle distributions at~2-6 keV and~50-75 keV, which are characteristic of drift-bounce resonances. Third, the lower-energy (<32 eV) ion flux is modulated at double the wave frequency, which are the result of E × B effect. Considering the generation mechanism of this poloidal mode wave within the plume, we find that it is likely generated by drift-bounce resonance from an unstable population of ions, due to an inward radial phase space density gradient. We suggest that the localization of waves to the plume is because the high plasma density reduces the local poloidal mode eigenfrequency, enabling a match to the drift-bounce frequencies of these ions, and resonant energy transfer from these particles to the eigenfunction at this location. This generates the Pc4-5 second harmonic poloidal waves at a much lower L region than would otherwise be expected. Key Points:• The high-m poloidal waves in the dawnside plume were observed by THEMIS-E • The inward radial gradient of~57 keV and higher plasma density enable the second harmonic poloidal wave to occur in the dawnside plume • Three types of particle flux modulations are observed simultaneously along with the wave in different energy bands Supporting Information:• Supporting Information S1

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Giant Pulsations Excited by a Steep Earthward Gradient of Proton Phase Space Density: Arase Observation

Cited by 11 publications

References 39 publications

Excitation of Internally Driven ULF Waves by the Drift‐Bounce Resonance With Ring Current Ions Based on the Drift‐Kinetic Simulation

Excitation of Internally Driven ULF Waves by the Drift‐Bounce Resonance With Ring Current Ions Based on the Drift‐Kinetic Simulation

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

Pc4‐5 Poloidal ULF Wave Observed in the Dawnside Plasmaspheric Plume

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