Statistical Properties of Pc4‐5 ULF Waves in Plasmaspheric Plumes.

Ultra‐low‐frequency (ULF) waves emerge as pivotal factors in elucidating the mechanisms that drive the intricate dynamics of radiation belt electrons within the plasmasphere and plasmaspheric plumes. Utilizing THEMIS data from September 2012 to September 2017, we conducted a comprehensive statistical analysis of Pc4‐5 ULF waves within and outside the plasmaspheric plume. Our findings reveal a distinctive dawn‐dusk asymmetry in occurrence rate and wave power of poloidal mode waves in the absence of the plume, resembling the toroidal mode asymmetry observed. Poloidal mode waves exhibit a higher likelihood of formation within the plume, while the toroidal mode waves show the opposite trend, contributing to the elevated dusk‐side occurrence rate of poloidal mode waves. Moreover, both wave modes within the plume demonstrate lower peak frequencies compared to waves outside the plume. The global distribution of wave power within the plume suggests higher power at noon than on the dusk side. Plain Language Summary: In this work, we report the statistical analysis of Pc4‐5 ULF waves both within and outside the plasmaspheric plume. We discovered a noticeable difference between the dawn and dusk sides in how often and how strongly poloidal and toroidal mode waves occur when the plasmaspheric plume is absent. Intriguingly, poloidal mode waves are more likely to form within the plume, while toroidal mode waves tend to do the opposite. This leads to a higher occurrence of poloidal mode waves on the dusk side. Additionally, both wave types within the plume have lower peak frequencies than those outside the plume. The power of both types of waves within the plasmaspheric plume, the toroidal and poloidal modes, is higher around noon compared to the dusk side. This indicates that the solar wind dynamic pressure and the plasmaspheric plume's connection with the flanks play a crucial role in creating and spreading ULF waves. Key Points: The Pc4‐5 ULF waves in the presence and absence of plasmaspheric plume at L ∼ 6–12 are statistically studied by THEMIS satellitesThe majority of waves within the plasmaspheric plume are poloidal waves, and the majority of waves outside the plasmaspheric plume are toroidal wavesThe plasmaspheric plume has a significant effect on the wave properties of poloidal mode waves and toroidal mode waves [ABSTRACT FROM AUTHOR]