A Statistical Examination of Interactions Between 1‐Hz Whistler Waves and Ions in the Earth's Foreshock.

Autor: Wang, Shan1 (AUTHOR) coralwang90@gmail.com, Li, Jing‐Huan1 (AUTHOR), Li, Li1 (AUTHOR), Zhou, Xu‐Zhi1 (AUTHOR), Omura, Yoshiharu2,3 (AUTHOR), Zhao, Jiu‐Tong1 (AUTHOR), Liu, Zhi‐Yang4 (AUTHOR), Zong, Qiu‐Gang1,3 (AUTHOR), Zhang, Hui5 (AUTHOR), Yue, Chao1 (AUTHOR)
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Zdroj: Journal of Geophysical Research. Space Physics. Oct2024, Vol. 129 Issue 10, p1-21. 21p.
Abstrakt: The 1 Hz whistler wave precursors attached to shock‐like structures are often observed in the foreshock. Using observations from the Magnetospheric Multiscale mission, we investigate the interactions between 1 Hz waves and ions. Incoming solar wind ions do not cyclotron‐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 theory and non‐linear trapping theory for non‐cyclotron‐resonant modulations. 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 of shock‐like structures. In one event, locally reflected ions exhibit non‐cyclotron‐resonant modulation in the early stage, and later approach the anomalous cyclotron 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, such as frequency dispersions, are observed, encouraging further investigations. Key Points: Solar wind ions do not gyro‐resonate with 1 Hz whistlers, while they commonly exhibit gyro‐phase bunching and Landau resonance with the waveSLAMS reflected ions show hints of gyro‐resonance with 1 Hz whistlers and losing energy to the fields, with aid of background B gradientWhistler‐ion interactions can cause ion reflections upstream of the main ramp, which in turn modifies shock‐like structures [ABSTRACT FROM AUTHOR]
Databáze: GreenFILE
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