Statistical Properties of EMIC Waves in Plasmaspheric Plumes and Their Particle Scattering Effects

Electromagnetic ion cyclotron (EMIC) waves act as a dominant driver causing the precipitation of relativistic electrons and ring current protons. Such precipitation process depends strongly on the wave properties and the ambient plasma environment. Although the statistical properties and associated particle scattering effects of EMIC waves have been extensively explored in the plasmasphere and plasmatrough, they remain unclear in plasmaspheric plumes. In this study, we statistically analyze EMIC waves in plasmaspheric plumes using Van Allen Probes observations. Our results show that most H + band EMIC waves occur in the afternoon sector at 5 < L < 7 with a peak occurrence of ∼8% at the magnetic local time (MLT) of ∼15, having lower wave normal angles (WNA) and left‐handed and linear polarity. Theoretical calculations predict that they can efficiently scatter relativistic electrons and energetic protons. Although He + band EMIC waves have similar properties and effects, they occur more frequently in a broader coverage of MLT with larger amplitudes and lower WNAs and ellipticities, and their effects are more pronounced. These results are critical for understanding the generation of EMIC waves and the associated particle scattering and loss process in plasmaspheric plumes, which are useful for future modeling of the magnetospheric plasma dynamics.