Magnetosonic Harmonic Falling and Rising Frequency Emissions Potentially Generated by Nonlinear Wave‐Wave Interactions in the Van Allen Radiation Belts
Magnetosonic Harmonic Falling and Rising Frequency Emissions Potentially Generated by Nonlinear Wave‐Wave Interactions in the Van Allen Radiation Belts
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DOI：
10.1029/2018gl079232
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发表时间：
2018-08
影响因子：
5.2
通讯作者：
N. Liu;Z. Su;Huinan Zheng;Yuming Wang;Shui Wang
中科院分区：
文献类型：
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作者：
N. Liu;Z. Su;Huinan Zheng;Yuming Wang;Shui Wang
磁声波在辐射带电子的复杂演化过程中起着潜在的重要作用。这些波通常出现为离散的发射线沿着质子回旋频率谐波，与预测的局部伯恩斯坦模式不稳定性的热质子环分布。磁声波几乎是无色散的，特别是在低次谐波处，因此在传播过程中具有大致不变的频率时间结构。根据货车艾伦探测器的观测结果，首次报道了磁声谐波的降频和升频发射。它们持续了2小时，主要发生在强亚暴后的向阳面等离子体。这些谐波发射线间隔很好的质子gyrofrequency，但表现出明显的下降（上升）的频率特性的质子gyrofrequency谐波的时间增加（减少）的制度。这种意想不到的结构可能是由质子回旋频率谐波的局部产生的磁声波和远离地球传播的恒定频率磁声波之间的非线性相互作用产生的。
Magnetosonic waves play a potentially important role in the complex evolution of the radiation belt electrons. These waves typically appear as discrete emission lines along the proton gyrofrequency harmonics, consistent with the prediction of the local Bernstein mode instability of hot proton ring distributions. Magnetosonic waves are nearly dispersionless particularly at low harmonics and therefore have the roughly unchanged frequency time structures during the propagation. On the basis of Van Allen Probes observations, we here present the first report of magnetosonic harmonic falling and rising frequency emissions. They lasted for up to 2 hr and occurred primarily in the dayside plasmatrough following intense substorms. These harmonic emission lines were well spaced by the proton gyrofrequency but exhibited a clear falling (rising) frequency characteristic in a regime with the temporal increase (decrease) of the proton gyrofrequency harmonics. Such unexpected structures might be produced by the nonlinear interactions between the locally generated magnetosonic waves at the proton gyrofrequency harmonics and a constant frequency magnetosonic wave propagating away from the Earth.