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- Title
Nonlinear Drift‐Bounce Resonance Between Charged Particles and Ultralow Frequency Waves.
- Authors
Li, Li; Zhou, Xu‐Zhi; Omura, Yoshiharu; Zong, Qiu‐Gang; Liu, Ying; Rankin, Robert; Yue, Chao; Zhuang, Yan; Ren, Jie; Wang, Shan; Fu, Sui‐Yan
- Abstract
Ultra‐low frequency (ULF) waves contribute significantly to the dynamic evolution of Earth's magnetosphere by accelerating and transporting charged particles within a wide energy range. A substantial excitation mechanism of these waves is their drift‐bounce resonant interactions with magnetospheric particles. Here, we extend the conventional drift‐bounce resonance theory to formulate the nonlinear particle trapping in the ULF wave‐carried potential well, which can be approximately described by a pendulum equation. We also predict the observable signatures of the nonlinear drift‐bounce resonance, and compare them with spacecraft observations. We further discuss potential drivers of the pendulum including the convection electric field and the magnetospheric dayside compression, which lead to additional particle acceleration or deceleration depending on magnetic longitude. These drivers indicate preferred regions for nonlinear ULF wave growth, which are consistent with previous statistical studies. Plain Language Summary: In Earth's magnetosphere, electromagnetic oscillations in the mHz frequency range referred to as ultra‐low frequency (ULF) waves have been frequently reported in space and ground‐based observations. These waves have been known to interact resonantly with magnetospheric particles during their drift and bounce motions, which plays a key role in the acceleration and transport of charged particles in the Van Allen radiation belts. Drift‐bounce resonance occurs when a resonant particle experiences repetitive patterns of the wave field over consecutive bounce cycles along its drift orbit, thus enabling a cumulative energy exchange between waves and particles. In previous studies of drift‐bounce resonance, a linearization approach is applied for simplicity. Here, we extend the conventional theory into the nonlinear regime, to formulate the nonlinear trapping of particles based on a pendulum equation and to predict the characteristic signatures of drift‐bounce resonance. Moreover, we discuss the potential drivers of the pendulum, including the magnetospheric convection and the dayside compression, which break the symmetry in the phase portrait of the particle trajectories and therefore, lead to continuous particle acceleration or deceleration depending on magnetic longitude. Our study on nonlinear drift‐bounce resonance is helpful to the understanding of the ULF wave‐particle interactions and the wave excitation processes. Key Points: A nonlinear framework for drift‐bounce resonance is developed to describe the particle behavior in Ultra‐low frequency (ULF) wavesNonlinear drift‐bounce resonance is characterized observationally by rolled‐up structures in particle pitch angle spectrumOur theory predicts that dayside and dusk sectors are preferred regions for nonlinear ULF wave growth
- Subjects
FREQUENCIES of oscillating systems; RADIATION belts; PARTICLE tracks (Nuclear physics); NONLINEAR waves; NONLINEAR theories; PARTICLE acceleration
- Publication
Journal of Geophysical Research. Space Physics, 2024, Vol 129, Issue 8, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2024JA032742