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Abstract Recent in situ observations from Parker Solar Probe (PSP) near perihelia reveal ion beams, temperature anisotropies, and kinetic wave activity. These features are likely linked to solar wind heating and acceleration. During PSP Encounter 17 (at 11.4Rs) on 2023 September 26, the PSP/FIELDS instrument detected enhanced ion-scale wave activity associated with deviations from local thermodynamic equilibrium in ion velocity distribution functions (VDFs) observed by the PSP/Solar Probe Analyzers-Ion. Dense beams (secondary populations) were present in the proton VDFs during this wave activity. Using bi-Maxwellian fits to the proton VDFs, we found that the density of the proton beam population increased during the wave activity and, unexpectedly, surpassed the core population at certain intervals. Interestingly, the wave power was reduced during the intervals when the beam population density exceeded the core density. The drift velocity of the beams decreases from 0.9 to 0.7 of the Alfvén speed, and the proton core shows a higher temperature anisotropy (T⊥/T∥ > 2.5) during these intervals. We conclude that the observations during these intervals are consistent with a reconnection event during a heliospheric current sheet crossing. During this event,α-particle parameters (density, velocity, and temperature anisotropy) remained nearly constant. Using linear analysis, we examined how the proton beam drives instability or wave dissipation. Furthermore, we investigated the nonlinear evolution of ion kinetic instabilities using hybrid kinetic simulations. This study provides direct clues about energy transfer between particles and waves in the young solar wind.
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This content will become publicly available on December 23, 2026
Energy Transfer from Magnetohydrodynamic-scale Slow-mode Waves to Kinetic-scale Ion Acoustic Waves
Abstract Large-amplitude slow-mode waves are commonly observed near Earth’s magnetopause. Recent observations show that these waves can occur simultaneously with kinetic-scale ion acoustic waves (IAWs). The amplitude of the IAWs is enhanced near the magnetic field peaks of the slow-mode wave, suggesting that the slow-mode waves may drive the generation of IAWs. To test this hypothesis, we conduct a hybrid simulation using observation-based parameters. The simulation results demonstrate that large-amplitude slow-mode waves generate counterstreaming ion beams, which in turn excite IAWs and relax the ion beams. Our study reveals a clear energy transfer channel from magnetohydrodynamic-scale slow-mode waves to kinetic-scale IAWs.
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- Award ID(s):
- 2108582
- PAR ID:
- 10710203
- Publisher / Repository:
- American Astronomical Society (AAS)
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 996
- Issue:
- 1
- ISSN:
- 2041-8205
- Page Range / eLocation ID:
- L8
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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