Fast magnetosonic (MS) waves have been found to propagate mainly in the radial direction inside the plasmasphere. One main topic about the radial propagation of MS waves is whether they would propagate down to the ground or be reflected at some regions. Since WKB assumption might become invalid near the reflection point (if the reflection happens), an analytic approach has been utilized to investigate the propagation behavior of MS waves in this study. It is found that as MS waves propagate inward into the Earth, they might reach the cut-off regions when their frequencies become close to the cut-off frequency. Moreover, as demonstrated by our theoretical model, the behavior of MS waves around these regions can be described by the Airy's equation. Our results find that MS waves would be fully reflected near the cut-off point, since only evanescent waves are allowed in the cut-off regions.

中文翻译：

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接近截止频率的快速磁声波的径向全反射

已发现快速磁超声 (MS) 波主要在等离子体层内沿径向传播。关于 MS 波径向传播的一个主要话题是它们是否会向下传播到地面或在某些区域被反射。由于 WKB 假设可能在反射点附近失效（如果发生反射），因此在本研究中采用了一种分析方法来研究 MS 波的传播行为。研究发现，当 MS 波向内传播到地球时，当它们的频率接近截止频率时，它们可能会到达截止区域。此外，正如我们的理论模型所证明的那样，这些区域周围的 MS 波的行为可以通过艾里方程来描述。我们的结果发现 MS 波会在截止点附近完全反射，