We investigate the reflection of low-harmonic fast magnetosonic (MS) waves at the local two-ion cutoff frequency ($f_{{\mathrm{cutHe}}^{+}}$). By comparing the wave signals of the two Van Allen Probes satellites, a distinct boundary where wave energies cannot penetrate inward are found in the time–frequency domain. The boundary is identified as the time series of local $f_{{\mathrm{cutHe}}^{+}}$. For a certain frequency, there exists a spatial interface formed by $f_{{\mathrm{cutHe}}^{+}}$, where the incident waves should be reflected. The waves with small incident angles are more likely to penetrate the thin layer where the group velocity reduces significantly and then slow down in a period of several to tens of seconds before the reflection process complete. The cutoff reflection scenario can explain the intense outward waves observed by probe A. These results of MS reflection at $f_{{\mathrm{cutHe}}^{+}}$ may help to predict the global distribution of MS waves and promote the understanding of wave–particle dynamics in the radiation belt.

中文翻译：

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低频快磁声波在局部二离子截止频率处的反射：在等离子体层中的观察

我们研究了低谐波快磁超声 (MS) 波在局部两离子截止频率 ($F_{{\mathrm{切他}}^{+}}$）。通过比较两颗 Van Allen Probes 卫星的波信号，在时频域中发现了波能无法向内穿透的明显边界。边界被识别为局部时间序列$F_{{\mathrm{切他}}^{+}}$. 对于某一频率，存在由$F_{{\mathrm{切他}}^{+}}$，入射波应该被反射。小入射角的波更有可能穿透群速度显着降低的薄层，然后在反射过程完成前的几秒到几十秒内减速。截止反射场景可以解释探针 A 观察到的强烈外向波。 这些 MS 反射结果在$F_{{\mathrm{切他}}^{+}}$ 可能有助于预测 MS 波的全球分布，促进对辐射带中波粒动力学的理解。