Relativistic electron scattering by large amplitude electromagnetic ion cyclotron waves: The role of phase bunching and trapping

Liu, Kaijun; Winske, D.; Gary, S. Peter; Reeves, G. D.

doi:10.1029/2011ja017476

Cited by 44 publications

(78 citation statements)

References 58 publications

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“…(3) When EMIC wave amplitudes are large, nonlinear resonant interactions can occur. The nonlinear phase bunching and/or trapping can reduce the loss of relativistic electrons and lead to a more flattened pitch angle distribution than that predicted by quasi‐linear theory [ Albert and Bortnik , ; Liu et al ., ]. We thus suggest that the discrepancy in our model result might be due to the relatively simplicity of our model, i.e., the adoption of the quasi‐linear resonant diffusion theory in a cold plasma.…”

Section: Summary and Discussionmentioning

confidence: 73%

Direct evidence for EMIC wave scattering of relativistic electrons in space

Zhang

et al. 2016

JGR Space Physics

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Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause efficient losses of highly relativistic (>1 MeV) electrons via gyroresonant interactions. Simultaneous observations of EMIC waves and equatorial electron pitch angle distributions, which can be used to directly quantify the EMIC wave scattering effect, are still very limited, however. In the present study, we evaluate the effect of EMIC waves on pitch angle scattering of ultrarelativistic (>1 MeV) electrons during the main phase of a geomagnetic storm, when intense EMIC wave activity was observed in situ (in the plasma plume region with high plasma density) on both Van Allen Probes. EMIC waves captured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and on the ground across the Canadian Array for Real‐time Investigations of Magnetic Activity (CARISMA) are also used to infer their magnetic local time (MLT) coverage. From the observed EMIC wave spectra and local plasma parameters, we compute wave diffusion rates and model the evolution of electron pitch angle distributions. By comparing model results with local observations of pitch angle distributions, we show direct, quantitative evidence of EMIC wave‐driven relativistic electron losses in the Earth's outer radiation belt.

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Section: Summary and Discussionmentioning

confidence: 73%

Direct evidence for EMIC wave scattering of relativistic electrons in space

Zhang

et al. 2016

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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“…Evaluations of bounce-averaged diffusion coefficients by multiband EMIC waves in the realistic hot plasma environment are important to acquire improved understanding of the role of EMIC waves in the processes of outer zone relativistic electron loss, especially during geomagnetically disturbed periods, which requires careful investigation in future studies. In addition, when EMIC wave amplitudes are large, nonlinear resonant interactions can occur, leading to advection toward large pitch angles [Albert and Bortnik, 2009] and flattening of pitch angle distribution caused by nonlinear phase trapping and bunching [Liu et al, 2012], both of which will reduce the precipitation losses of relativistic electrons. The nonlinear interaction between highly intense EMIC waves and radiation belt relativistic electrons is another subject that is left as a future study.…”

Section: 1002/2015ja021466mentioning

confidence: 99%

Resonant scattering of outer zone relativistic electrons by multiband EMIC waves and resultant electron loss time scales

et al. 2015

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To improve our understanding of the role of electromagnetic ion cyclotron (EMIC) waves in radiation belt electron dynamics, we perform a comprehensive analysis of EMIC wave‐induced resonant scattering of outer zone relativistic (>0.5 MeV) electrons and resultant electron loss time scales with respect to EMIC wave band, L shell, and wave normal angle model. The results demonstrate that while H+‐band EMIC waves dominate the scattering losses of ~1–4 MeV outer zone relativistic electrons, it is He+‐band and O+‐band waves that prevail over the pitch angle diffusion of ultrarelativistic electrons at higher energies. Given the wave amplitude, EMIC waves at higher L shells tend to resonantly interact with a larger population of outer zone relativistic electrons and drive their pitch angle scattering more efficiently. Obliquity of EMIC waves can reduce the efficiency of wave‐induced relativistic electron pitch angle scattering. Compared to the frequently adopted parallel or quasi‐parallel model, use of the latitudinally varying wave normal angle model produces the largest decrease in H+‐band EMIC wave scattering rates at pitch angles < ~40° for electrons > ~5 MeV. At a representative nominal amplitude of 1 nT, EMIC wave scattering produces the equilibrium state (i.e., the lowest normal mode under which electrons at the same energy but different pitch angles decay exponentially on the same time scale) of outer belt relativistic electrons within several to tens of minutes and the following exponential decay extending to higher pitch angles on time scales from <1 min to ~1 h. The electron loss cone can be either empty as a result of the weak diffusion or heavily/fully filled due to approaching the strong diffusion limit, while the trapped electron population at high pitch angles close to 90° remains intact because of no resonant scattering. In this manner, EMIC wave scattering has the potential to deepen the anisotropic distribution of outer zone relativistic electrons by reshaping their pitch angle profiles to “top‐hat.” Overall, H+‐band and He+‐band EMIC waves are most efficient in producing the pitch angle scattering loss of relativistic electrons at ~1–2 MeV. In contrast, the presence of O+‐band EMIC waves, while at a smaller occurrence rate, can dominate the scattering loss of 5–10 MeV electrons in the entire region of the outer zone, which should be considered in future modeling of the outer zone relativistic electron dynamics.

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Relativistic electron scattering by large amplitude electromagnetic ion cyclotron waves: The role of phase bunching and trapping

Cited by 44 publications

References 58 publications

Direct evidence for EMIC wave scattering of relativistic electrons in space

Direct evidence for EMIC wave scattering of relativistic electrons in space

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

Resonant scattering of outer zone relativistic electrons by multiband EMIC waves and resultant electron loss time scales

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