Parametric Dependence of Polarization Reversal Effects on the Particle Pitch Angle Scattering by EMIC Waves

Lou, Yunjiang; Cao, Xing; Ni, Binbin; Wu, Mingyu; Zhang, Tielong

doi:10.1029/2021ja029966

Cited by 6 publications

(3 citation statements)

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“…(2020) and Lou et al. (2021) further confirmed that inclusion of polarization reversal of EMIC waves at higher latitudes weakens the pitch angle scattering efficiency of ring current protons. Furthermore, proton precipitations into the atmosphere due to EMIC wave scattering can result in the formation of detached proton arcs at subauroral latitudes (Fuselier et al., 2004; Spasojevic et al., 2011; Su et al., 2011) and the reversed energy‐latitude type of ion precipitation boundary (Cao et al., 2016; Liang et al., 2014), as well as local density disturbances in the E‐region (∼100–150 km) ionosphere (Tian et al., 2023).…”

Section: Introductionmentioning

confidence: 77%

Comparison of Ring Current Proton Losses Between Contributions From Scattering by Field Line Curvature and EMIC Waves

Cao,

Ni,

et al. 2023

JGR Space Physics

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Although both the field line curvature (FLC) and electromagnetic ion cyclotron (EMIC) waves are recognized to contribute importantly to the loss of energetic protons in the Earth's ring current, their quantitative differences in scattering ring current protons are still not fully understood. In this study, using a realistic, nondipolar magnetic field model, we perform a detailed analysis of the scattering effects of ring current protons and the resultant proton lifetimes due to FLC and EMIC waves at different L‐shells under different levels of geomagnetic activity. We find that compared with EMIC wave‐driven scattering, FLC scattering has a stronger dependence on L‐shell and geomagnetic activity. Pitch angle scattering efficiency due to FLC enhances significantly as proton energy increases. In contrast, scattering by H+ band EMIC waves tends to be weaker with increasing proton energy, while the scattering rates by He+ band EMIC waves increase first and then decrease. The results of proton lifetime against pitch angle scattering show that EMIC wave‐driven scattering dominates the loss of ring current protons at lower L‐shells (L < 6), especially during geomagnetically quiet conditions. During geomagnetically active conditions at L ≥ 6, EMIC wave‐driven scattering dominates at lower proton energies, while FLC scattering dominates at higher proton energies. This study improves the current understanding of the relative contributions of scattering by FLC and EMIC waves to the Earth's ring current proton dynamics.

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Section: Introductionmentioning

confidence: 77%

Comparison of Ring Current Proton Losses Between Contributions From Scattering by Field Line Curvature and EMIC Waves

Cao,

Ni,

et al. 2023

JGR Space Physics

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“…In addition, the pitch angle scattering efficiency may be affected by its polarization property. Previous simulation studies have shown that polarization reversal of H + ‐band EMIC waves could cause more efficient scattering of relativistic electrons (e.g., Cao et al., 2020; Lou et al., 2021). As shown in Figures 2e and 2f, the first and the third EMIC waves are linearly polarized, while the second EMIC wave is left‐hand polarized with smaller wave normal angles.…”

Section: Discussionmentioning

confidence: 99%

“…Recently, Zhu et al (2020) reported a compression-induced EMIC wave event and provided direct evidence of pitch angle scattering of relativistic electrons by EMIC waves. In addition, a variety of studies tried to figure out the factors that influence the pitch angle scattering efficiency of relativistic electrons by EMIC waves and find that plasma wave parameters can affect the wave-particle interaction between EMIC waves and relativistic electrons, such as wave amplitude, the ellipticity of polarization, wave normal angle and wave frequency (Cao et al, 2020;Lou et al, 2021;Qin et al, 2020;Silin et al, 2011;. Cao et al (2020) conducted a simulation study and concluded that polarization reversal has an important impact on the pitch angle diffusion coefficients induced by H + -band EMIC waves, but not He + -band EMIC waves.…”

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confidence: 99%

Prompt Appearance of Large‐Amplitude EMIC Waves Induced by Solar Wind Dynamic Pressure Enhancement and the Subsequent Relativistic Electron Precipitation

et al. 2023

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Electromagnetic ion cyclotron (EMIC) waves play an important role in relativistic electron dynamics. In this study, we find a large‐amplitude EMIC wave event induced by the prompt enhancement of solar wind dynamic pressure on 6 November 2015. These large‐amplitude EMIC waves are simultaneously observed by multiple satellites over 13 hr in magnetic local time (MLT) with a peak amplitude of ∼4 nT. Satellites at different locations observed different bands of EMIC waves, implying the importance of background plasma density in EMIC wave generation. Electron pitch angle distributions show obvious responses to EMIC wave activities. During EMIC wave appearance, the fluxes of relativistic electrons with pitch angles around 90° increase, while the fluxes of field‐aligned relativistic electrons decrease, showing distinct “bite‐out” signatures, indicating pitch angle scattering by EMIC waves, and the scattering efficiency depends on the amplitude and polarization of EMIC waves. Combined with phase space density profiles of electrons that are nearly constant at energies below the minimum resonant energy of electrons (Emin) but show dropout at energies above the Emin after EMIC wave activities, we conclude that large‐amplitude EMIC waves can cause rapid electron loss down to several hundred keV. In addition, simultaneous observations of hundreds of keV electron precipitation and tens of keV proton precipitation by Polar Operational Environmental Satellites near the region where EMIC waves are observed, provide direct evidence of relativistic electron precipitation caused by the large‐amplitude EMIC waves, ultimately driven by solar wind structures.

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Influence of Initial Proton Energy on the Nonlinear Interactions Between Ring Current Protons and He⁺ Band EMIC Waves

Zhou,

Cai

2024

JGR Space Physics

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The energy of ring current protons is believed to influence the pitch angle scattering due to electromagnetic ion cyclotron (EMIC) waves and is typically analyzed using quasi‐linear theory. However, nonlinear behavior becomes significant as the wave amplitude intensifies. In this study, we aim to explore how the nonlinear behavior depends on the initial proton energy under various background plasma density conditions. The frequency of EMIC waves is 0.96ΩHe (where ΩHe is the gyrofrequency of He+ at the equator). It is found that the higher energy protons with nonlinear phase trapping experience more resonances, causing these trapped protons to move away from the loss cone more quickly compared to lower energy protons. However, the proportion of phase‐trapped protons significantly decreases as the initial proton energy increases. This declining trend is more pronounced for a background plasma condition in the plasmapause than within the plasmasphere. The number of phase‐trapped protons goes to zero as initial proton energy increases to above approximately 60 keV. Additionally, nonlinear phase bunching is more pronounced for lower energy protons (e.g., below 60 keV) compared to higher energy protons. As a result, both nonlinear phase trapping and phase bunching contribute to larger standard deviations in the net changes of equatorial pitch angle (Δαeq), suggesting a larger pitch agnel diffusion coefficient compared to the prediction of quasi‐linear theory.

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Parametric Dependence of Polarization Reversal Effects on the Particle Pitch Angle Scattering by EMIC Waves

Abstract: EMIC waves can pitch angle scatter radiation belt electrons and ring current protons rapidly into the loss cone via cyclotron resonance, leading to the electron dropout in the radiation belts and proton aurora at subauroral latitudes (

Cited by 6 publications

References 66 publications

Comparison of Ring Current Proton Losses Between Contributions From Scattering by Field Line Curvature and EMIC Waves

Comparison of Ring Current Proton Losses Between Contributions From Scattering by Field Line Curvature and EMIC Waves

Prompt Appearance of Large‐Amplitude EMIC Waves Induced by Solar Wind Dynamic Pressure Enhancement and the Subsequent Relativistic Electron Precipitation

Influence of Initial Proton Energy on the Nonlinear Interactions Between Ring Current Protons and He⁺ Band EMIC Waves

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Parametric Dependence of Polarization Reversal Effects on the Particle Pitch Angle Scattering by EMIC Waves

Abstract: EMIC waves can pitch angle scatter radiation belt electrons and ring current protons rapidly into the loss cone via cyclotron resonance, leading to the electron dropout in the radiation belts and proton aurora at subauroral latitudes (

Cited by 6 publications

References 66 publications

Comparison of Ring Current Proton Losses Between Contributions From Scattering by Field Line Curvature and EMIC Waves

Comparison of Ring Current Proton Losses Between Contributions From Scattering by Field Line Curvature and EMIC Waves

Prompt Appearance of Large‐Amplitude EMIC Waves Induced by Solar Wind Dynamic Pressure Enhancement and the Subsequent Relativistic Electron Precipitation

Influence of Initial Proton Energy on the Nonlinear Interactions Between Ring Current Protons and He+ Band EMIC Waves

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Influence of Initial Proton Energy on the Nonlinear Interactions Between Ring Current Protons and He⁺ Band EMIC Waves