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A statistical examination of ion dynamics at 1-Hz whistler waves in the Earth's foreshock
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  • Shan Wang,
  • Jing-Huan Li,
  • Li Li,
  • Xu-Zhi Zhou,
  • Yoshiharu Omura,
  • Jiutong Zhao,
  • Zhi-Yang Liu,
  • Qiu-Gang Zong,
  • Hui Zhang,
  • Chao Yue
Shan Wang
Peking University

Corresponding Author:[email protected]

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Jing-Huan Li
Peking University
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Li Li
Peking University
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Xu-Zhi Zhou
Peking University
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Yoshiharu Omura
Kyoto University
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Jiutong Zhao
Peking University
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Zhi-Yang Liu
Institut de Recherche en Astrophysique et Planétologie (IRAP)
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Qiu-Gang Zong
Peking University
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Hui Zhang
University of Alaska Fairbanks
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Chao Yue
Peking Univeristy
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Abstract

The 1-Hz whistler wave precursor attached to shock-like structures are often observed in foreshock. Using observations from the Magnetospheric Multiscale mission, we investigate the interactions between 1-Hz waves and ions. Incoming solar wind ions do not gyro-resonate with the wave, since typically the wave is right-handed in their frame. We demonstrate that solar wind ions commonly exhibit 180 gyro-phase bunching from the wave magnetic field, understanding it with a reconciled linear picture for non-resonant ions and non-linear trapping theory of anomalous resonance. Along the longitudinal direction, solar wind ions experience Landau resonance, exhibiting either modulations at small wave potentials or trapping in phase-space holes at large potentials. The results also improve our understanding of foreshock structure evolution and 1-Hz wave excitation. Shock-like structures start with having incoming solar wind and remotely-reflected ions from further downstream. The ion-scale 1-Hz waves can already appear during this stage. The excitation may be due to shock-like dispersive radiation or kinetic instabilities resonant with these remotely-reflected ions. Ions reflected by local shock-like structures occur later, so they are not always necessary for generating 1-Hz waves. The wave leads to ion reflection further upstream, which may cause reformation. In one event, locally-reflected ions exhibit anomalous resonance in the early stage, and later approach to the gyro-resonant condition with gyro-phases ~270 . The latter is possibly due to nonlinear trapping in regions with an upstream-pointing magnetic field gradient, linked to reformation. Some additional special features like frequency dispersions are observed, requiring better explanations in the future.
13 Jun 2024Submitted to ESS Open Archive
13 Jun 2024Published in ESS Open Archive