We present Van Allen Probes observations of a long-lasting ULF wave event with frequency doubling features in the compressional wave component. The azimuthal magnetic field, on the other hand, shows shoulder-like pulsations characterized by the presence of two bumps between the crests and troughs within each wave cycle. A wavelet analysis suggests that the shoulder-like pulsations originate from a secondary peak of the wave power at a frequency of three times the dominant wave frequency. Shoulder-like pulsations have been observed in many ULF wave events with frequency doubling features, although this phenomenon has never been reported or explained. Here, we propose that these features can be caused by monochromatic oscillations of the magnetic flux tubes in a ballooning-mirror mode structure. Then, a simple model is developed to reproduce these signatures, which also has the potential to yield uneven bumps in shoulder-like pulsations depending on the spacecraft location.

中文翻译：

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ULF波中倍频和肩状磁脉动的起源

我们展示了 Van Allen Probes 对压缩波分量中具有倍频特征的持久超低频波事件的观察结果。另一方面，方位磁场显示肩状脉动，其特征是在每个波周期内波峰和波谷之间存在两个凸起。小波分析表明，肩状脉动起源于波功率的次要峰值，频率是主波频率的三倍。在许多具有倍频特征的超低频波事件中已经观察到肩状脉动，尽管这种现象从未被报道或解释过。在这里，我们提出这些特征可能是由气球镜模式结构中磁通量管的单色振荡引起的。然后，