“…Energy input to Earth's magnetosphere from the Sun is controlled by solar wind and interplanetary magnetic field, part of which is mediated by ultralow‐frequency (ULF) waves in the frequency range of 1 mHz to 1 Hz. ULF waves can propagate electromagnetic energy over the magnetosphere and into the ionosphere and play a crucial role in the acceleration and transportation of energetic particles in the radiation belt and ring current (e.g., Claudepierre et al, ; Mann, ; Min et al, ; Takahashi et al, ; Ukhorskiy et al, ; Zong, Rankin, et al, ) and cold particles in the plasmasphere (e.g., Ren, Zong, Miyoshi, et al, ; Ren et al, ; Yue et al, ; Zong, Wang, et al, ). Previous studies have demonstrated that the drift‐bounce resonant particles around the magnetic equator exhibit bidirectional pitch angle distributions (e.g., Ren et al, ; Takahashi et al, ; Yang, Zong, Fu, Takahashi, et al, ), and the off‐equator resonant particles will show pitch angle dispersion signatures (e.g., Ren, Zong, Zhou, et al, ; Yang, Zong, Fu, Takahashi, et al, ).…”