Parametric dependence of polarization reversal effects on the particle pitch angle scattering by EMIC waves

Electromagnetic ion cyclotron (EMIC) waves play an important role in the loss of both radiation belt electrons and ring current protons. After EMIC waves are excited near the magnetic equator, they will propagate to high latitudes and suffer a polarization reversal from left-handed to right-handed polarized at the crossover frequency. In this study, to improve the current understanding of the EMIC wave-induced loss of radiation belt electrons and ring current protons, we perform a detailed analysis of the sensitivity of polarization reversal effects to L-shell, electron number density, and wave frequency spectrum. Our results show that polarization reversal contributes significantly to the pitch angle diffusion coefficients at low pitch angles extending to the loss cone angle for various parameter sets. The inclusion of polarization reversal mainly enhances the electron scattering loss at several MeV and weaken the proton scattering loss over a broad energy range from a few keV to 1 MeV. While the increase of electron diffusion coefficients can be up to a factor of 5, the decrease of proton diffusion coefficients can be larger than an order of magnitude. As L-shell or electron density increases, the affected resonant region by polarization reversal for both electrons and protons tends to expand to lower energies, while an increase of peak wave frequency will shift the resonant region to higher energies. Our results confirm the vital importance of including polarization reversal in understanding the EMIC wave-induced scattering loss of radiation belt electrons and ring current protons. <br>

电磁离子回旋波（Electromagnetic ion cyclotron, EMIC）在辐射带电子与环电流质子的损失过程中发挥着重要作用。当电磁离子回旋波在磁赤道附近激发后，会向高纬度传播，并在交叉频率处发生从左旋偏振到右旋偏振的偏振反转。本研究为深化对电磁离子回旋波诱导的辐射带电子与环电流质子损失过程的认知，针对偏振反转效应与L壳层、电子数密度及波频谱的敏感性开展了详细分析。研究结果表明，在多组参数设定下，偏振反转对延伸至损失锥角的低投角区域的投角扩散系数具有显著贡献。引入偏振反转效应后，主要增强数兆电子伏特能区的电子散射损失，同时在数千电子伏特至1兆电子伏特的宽能量范围内削弱质子散射损失。电子扩散系数的增幅最高可达5倍，而质子扩散系数的降幅则可超过一个数量级。随着L壳层或电子数密度的升高，偏振反转所影响的共振区域在电子与质子体系中均倾向于向更低能量方向拓展；而峰值波频率的升高则会将共振区域移至更高能量区间。本研究结果证实，在解析电磁离子回旋波诱导的辐射带电子与环电流质子散射损失过程时，纳入偏振反转效应至关重要。