Nonlinear pitch angle scattering of relativistic electrons by EMIC waves in the inner magnetosphere

Omura, Yoshiharu; Zhao, Qinghua

doi:10.1029/2012ja017943

Cited by 114 publications

(164 citation statements)

References 27 publications

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“…A subject area of current interest is that of resonant wave‐particle interaction between relativistic electrons and narrow band electromagnetic ion cyclotron (EMIC) “triggered emissions” [ Pickett et al , ; Omura et al , ]. Studies assuming parallel propagation find very effective precipitation of MeV electrons [ Omura and Zhao , , ]. The code here may be modified, by inserting heavy ions, to enable investigation of nonlinear wpi between relativistic electrons and obliquely propagating EMIC waves with either right‐handed or left‐handed polarization.…”

Section: Discussionmentioning

confidence: 99%

A computational and theoretical investigation of nonlinear wave‐particle interactions in oblique whistlers

Nunn

Omura

2015

JGR Space Physics

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Most previous work on nonlinear wave-particle interactions between energetic electrons and VLF waves in the Earth's magnetosphere has assumed parallel propagation, the underlying mechanism being nonlinear trapping of cyclotron resonant electrons in a parabolic magnetic field inhomogeneity. Here nonlinear wave-particle interaction in oblique whistlers in the Earth's magnetosphere is investigated. The study is nonself-consistent and assumes an arbitrarily chosen wave field. We employ a "continuous wave" wave field with constant frequency and amplitude, and a model for an individual VLF chorus element. We derive the equations of motion and trapping conditions in oblique whistlers. The resonant particle distribution function, resonant current, and nonlinear growth rate are computed as functions of position and time. For all resonances of order n, resonant electrons obey the trapping equation, and provided the wave amplitude is big enough for the prevailing obliquity, nonlinearity manifests itself by a "hole" or "hill" in distribution function, depending on the zero-order distribution function and on position. A key finding is that the n = 1 resonance is relatively unaffected by moderate obliquity up to 25°, but growth rates roll off rapidly at high obliquity. The n = 1 resonance saturates due to the adiabatic effect and here reaches a maximum growth at~20 pT, 2000 km from the equator. Damping due to the n = 0 resonance is not subject to adiabatic effects and maximizes at some 8000 km from the equator at an obliquity~55°.

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Section: Discussionmentioning

confidence: 99%

A computational and theoretical investigation of nonlinear wave‐particle interactions in oblique whistlers

Nunn

Omura

2015

JGR Space Physics

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“…Nonlinear resonant interaction has also been considered recently, leading to advection toward large pitch angles [ Albert and Bortnik , ] and flattening of pitch angle distribution caused by nonlinear phase trapping and bunching [ Liu et al , ], both of which will reduce the precipitation losses of relativistic electrons. However, nonlinear scattering due to EMIC waves with a rising tone might induce burst precipitation losses, especially with repeated interaction with a series of wave packets [ Omura and Zhao , ].…”

Section: Discussionmentioning

confidence: 99%

An improved dispersion relation for parallel propagating electromagnetic waves in warm plasmas: Application to electron scattering

et al. 2013

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[1] An improved dispersion relation, with thermal corrections retained, for parallel propagating electromagnetic waves in a warm plasma is developed for both left-hand (L-) and right-hand (R-) polarized modes. Compared with the cold plasma dispersion relation, the derived dispersion relation is in much better agreement with the full hot plasma dispersion relation (including the wave growth rate). The pitch angle scattering rates of energetic electrons are compared between using cold and full dispersion relation. Significant differences are found when evaluating pitch angle scattering rate of MeV electron caused by He + band waves in multiple ion plasmas. Due to He + ion cyclotron absorption, the He + band electromagnetic ion cyclotron waves, which are able to resonate with MeV electrons (at large wave number), tend to be strongly suppressed. Less significant differences in scattering rate of electrons between using cold and hot dispersion relation are found in the case of L-mode waves in single H + ion plasma and in the case of R-mode waves.

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“…In this event, EMIC emissions have significantly large amplitude and clear fine structures such as a rising frequency and an amplitude modulation (subpacket). Omura and Zhao (2012) have derived the threshold amplitude for nonlinear trapping of resonant electrons. They have performed test particle simulations of 0.1-to 10-MeV electrons with an EMIC rising tone with the amplitude of 2% of the magnitude of background magnetic field and the frequency rising from 0.5 to 0.8 proton gyrofrequency.…”

Section: 1029/2019ja026772mentioning

confidence: 99%

Rapid Precipitation of Relativistic Electron by EMIC Rising‐Tone Emissions Observed by the Van Allen Probes

et al. 2019

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On 23 February 2014, Van Allen Probes sensors observed quite strong electromagnetic ion cyclotron (EMIC) waves in the outer dayside magnetosphere. The maximum amplitude was more than 14 nT, comparable to 7% of the magnitude of the ambient magnetic field. The EMIC waves consisted of a series of coherent rising tone emissions. Rising tones are excited sporadically by energetic protons. At the same time, the probes detected drastic fluctuations in fluxes of MeV electrons. It was found that the electron fluxes decreased by more than 30% during the 1 min following the observation of each EMIC rising tone emissions. Furthermore, it is concluded that the flux reduction is a nonadiabatic (irreversible) process since holes in the particle flux levels appear as drift echoes with energy dispersion. We examine the process of electron pitch angle scattering by nonlinear wave trapping due to anomalous cyclotron resonance with EMIC rising tone emissions. The energy range of precipitated electrons agrees with the presumed energy for the threshold amplitude for nonlinear wave trapping. This is the first report of rapid precipitation (<1 min) of relativistic electrons by EMIC rising tone emissions and their drift echoes in time observed by spacecraft.

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Nonlinear pitch angle scattering of relativistic electrons by EMIC waves in the inner magnetosphere

Cited by 114 publications

References 27 publications

A computational and theoretical investigation of nonlinear wave‐particle interactions in oblique whistlers

A computational and theoretical investigation of nonlinear wave‐particle interactions in oblique whistlers

An improved dispersion relation for parallel propagating electromagnetic waves in warm plasmas: Application to electron scattering

Rapid Precipitation of Relativistic Electron by EMIC Rising‐Tone Emissions Observed by the Van Allen Probes

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