Van Allen Probes Observations of Symmetric Stormtime Compressional ULF Waves

Takahashi, Kazue; Crabtree, Chris; Ukhorskiy, A. Y.; Boyd, A. J.; Denton, R. E.; Turner, D. L.; Gkioulidou, M.; Vellante, M.

doi:10.1029/2021ja030115

Cited by 9 publications

(14 citation statements)

References 99 publications

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“…The symmetric ULF waves are excited outside of the plasma sphere, and localized in MLT and radial distance. The large amplitude (δB/B 0 0.1) and compressional nature of the fluctuation described by Takahashi et al (2022) are consistent with the one used for the acceleration process presented in Section 3.4. Moreover, the waves are observed in association with the injection of particles, and thus symmetric fluctuations are associated with local radial enhancements of particles.…”

Section: Higher-order Parker Mechanismsupporting

confidence: 83%

“…The observational signature of local wave-particle processes in the phase-space density consists of localized enhancements, whereas ULF radial diffusion results in the flattening of the phase-space density along the radial distance (Green & Kivelson 2004;Reeves et al 2013). When including higherorder terms in the radial transport equation, we found that seed electrons with 50-100 keV injected in the outer belts can experience additional betatron acceleration in the presence of symmetric ULF wave amplitudes with amplitudes comparable to the one reported by Takahashi et al (2022). This impulsive and convective higher-order process requires no drift resonance yet results in a localized enhancement of the phase-space density on timescales that are much shorter than the drift period.…”

Section: Discussionsupporting

confidence: 72%

“…Are symmetric ULF fluctuations observed in the Earth's radiation belts? In a recent observational study, Takahashi et al (2022) provide the first description of symmetric compressional 35 On the basis of Occam's razor argument (Popper 2005) we would favor a phase-mixing mechanism of nonresonant particles to explain the formation of zebra stripes. For instance, the observation of zebra stripes in both electron and proton fluxes in Saturn's magnetosphere (Sun et al 2022) is more easily explained through nonresonant processes.…”

Section: Higher-order Parker Mechanismmentioning

confidence: 99%

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Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Osmane,

Kilpua,

George

et al. 2023

ApJS

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Observational studies of the Earth’s radiation belts indicate that Alfvénic fluctuations in the frequency range of 2–25 mHz accelerate electrons to relativistic energies. For decades, statistical models of radiation belts have quantified the impact of Alfvénic waves in terms of quasi-linear diffusion. However, quasi-linear models are inadequate to quantify Alfvénic radial transport occurring on timescales comparable to the azimuthal drift period of 0.1–10 MeV electrons. With recent advances in observational methodologies offering coverage of the Earth’s radiation belts on fast timescales, a theoretical framework that distinguishes between fast and diffusive radial transport can be tested for the first time in situ. In this report, we present a drift-kinetic description of radial transport for planetary radiation belts. We characterize fast linear processes and determine the conditions under which higher-order effects become dynamically significant. In the linear regime, wave–particle interactions are categorized in terms of resonant and nonresonant responses. We demonstrate that the phenomenon of zebra stripes is nonresonant and can originate from injection events in the inner radiation belts. We derive a radial diffusion coefficient for a field model that satisfies Faraday’s law and that contains two terms: one scaling as L 10 independent of the azimuthal number m, and a second scaling as m 2 L 6. In the higher-order regime, azimuthally symmetric waves with properties consistent with in situ measurements can energize 10–100 keV electrons in less than a drift period. This process provides new evidence that acceleration by Alfvénic waves in radiation belts cannot be fully contained within diffusive models.

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Section: Higher-order Parker Mechanismsupporting

confidence: 83%

Section: Discussionsupporting

confidence: 72%

Section: Higher-order Parker Mechanismmentioning

confidence: 99%

See 1 more Smart Citation

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Osmane,

Kilpua,

George

et al. 2023

ApJS

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“…Near the equator, where odd transverse magnetic field variations have a node and field‐aligned variations have an antinode, the compressional component becomes the largest. Second and third, there are DMM and DCM obtained from kinetic theory (Takahashi et al., 2022). Chelpanov et al.…”

Section: Resultsmentioning

confidence: 99%

“…Near the equator, where odd transverse magnetic field variations have a node and field-aligned variations have an antinode, the compressional component becomes the largest. Second and third, there are DMM and DCM obtained from kinetic theory (Takahashi et al, 2022). Chelpanov et al (2018) used ground-based Ekaterinburg decameter radar (Berngardt et al, 2020) to analyze Pc5 waves frequency properties and found that the significant number of detected waves cannot be attributed to Alfvén waves, and DMM or DCM is the most probable interpretation.…”

Section: Compressional Wavesmentioning

confidence: 99%

Polarization and Spatial Distribution Features of Pc4 and Pc5 Waves in the Magnetosphere

Rubtsov,

Nosé,

Matsuoka

et al. 2023

JGR Space Physics

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Ultra‐low frequency waves interact with different particle populations all over the magnetosphere. Some interaction mechanisms are associated with certain wave modes, but is it really so and what about waves interaction between each other? We present a statistical analysis of Pc4 and Pc5 waves in the magnetosphere of the Earth that were observed by Arase satellite from March 2017 to December 2020. These waves were classified by polarization into toroidal, poloidal, and compressional waves. Toroidal and poloidal waves are thought to be Alfvén waves that are eigenoscillations of Earth’s magnetic field lines. The former are believed to be generated by external sources, while the latter one — by internal sources. We compared spatial distribution features with well‐known case studies to reveal their nature for all three polarizations. A high inclination of Arase orbit supported a wave field‐aligned structure research. We found that toroidal waves are mostly odd harmonics and poloidal waves are both even and odd harmonics of Alfvén waves, while compressional waves were observed in a narrow equatorial region only. Different wave generation mechanisms that cause a clear difference in spatial distributions of toroidal, poloidal, and compressional waves could excite a specific wave polarization. Surprisingly, a statistics of wave polarization has a normal distribution without separate clusters. We suggest that polarization change and mode coupling processes make mixed polarization the most common type of polarization in the magnetosphere. This result raises the question of how the polarization change process affects wave‐particles interactions responsible for energy transport throughout the magnetosphere.

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THEMIS observations of compressional Pc5 pulsations in the dawn- and duskside magnetosphere

Korotova,

Sibeck

2024

Advances in Space Research

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Van Allen Probes Observations of Symmetric Stormtime Compressional ULF Waves

Abstract: Ultralow-frequency (ULF) waves in the Pc4-5 band (period = 45-600 s) with strong radial and compressional magnetic field components (compressional poloidal waves) are observed at L > 5 within the ring current region (L = 3-8) during geomagnetic storms (

Cited by 9 publications

References 99 publications

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Polarization and Spatial Distribution Features of Pc4 and Pc5 Waves in the Magnetosphere

THEMIS observations of compressional Pc5 pulsations in the dawn- and duskside magnetosphere

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