Full-wave modeling of EMIC wave packets: ducted propagation and reflected waves
Full-wave modeling of EMIC wave packets: ducted propagation and reflected waves
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DOI：
10.3389/fspas.2023.1251563
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发表时间：
2023-10
影响因子：
3
通讯作者：
M. Hanzelka;Wen Li;Qianli Ma;Murong Qin;Xiao‐Chen Shen;L. Capannolo;L. Gan
中科院分区：
文献类型：
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作者：
M. Hanzelka;Wen Li;Qianli Ma;Murong Qin;Xiao‐Chen Shen;L. Capannolo;L. Gan
电磁离子回旋(EMIC)波可以散射能量在几百keV以上的辐射带电子。为了准确预测这些相对论电子在短时间尺度上的散射和由此产生的降水，我们需要详细了解波场的时空演变，而这不是单航天器测量所能获得的。我们的研究提供了在地球偶极磁场中从二维(2D)的时域有限差分(FDTD)模拟得到的EMIC波模型。我们研究了氢带和氦带波的传播、上升音发射、具有幅度调制的包和导管波的情况。我们分析了波在时间域中的传播特性，使之能够与现场观测进行比较。结果表明，冷等离子体密度梯度可以使波矢保持准平行，有效地引导波能，并对模式转换和反射产生深远影响。非导波的波法向角随纬度迅速增大，在离子混合频率上产生反射，不利于向低空传播。模拟的波场可以作为相对论电子和高能离子散射和沉淀的测试粒子分析的输入。
Electromagnetic ion cyclotron (EMIC) waves can scatter radiation belt electrons with energies of a few hundred keV and higher. To accurately predict this scattering and the resulting precipitation of these relativistic electrons on short time scales, we need detailed knowledge of the wave field’s spatio-temporal evolution, which cannot be obtained from single spacecraft measurements. Our study presents EMIC wave models obtained from two-dimensional (2D) finite-difference time-domain (FDTD) simulations in the Earth’s dipole magnetic field. We study cases of hydrogen band and helium band wave propagation, rising-tone emissions, packets with amplitude modulations, and ducted waves. We analyze the wave propagation properties in the time domain, enabling comparison with in situ observations. We show that cold plasma density gradients can keep the wave vector quasiparallel, guide the wave energy efficiently, and have a profound effect on mode conversion and reflections. The wave normal angle of unducted waves increases rapidly with latitude, resulting in reflection on the ion hybrid frequency, which prohibits propagation to low altitudes. The modeled wave fields can serve as an input for test-particle analysis of scattering and precipitation of relativistic electrons and energetic ions.