Energy transfer from MHD-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. The amplitude of the ion acoustic waves is enhanced near the magnetic field peaks of the slow-mode wave, suggesting that the slow-mode waves may drive the generation of ion acoustic waves. To test this hypothesis, we conduct a hybrid simulation using observation-based parameters. The simulation results demonstrate that large-amplitude slow-mode waves generate counter-streaming ion beams, which in turn excite ion acoustic waves and relax the ion beams. Our study reveals a clear energy transfer channel from MHD-scale slow-mode waves to kinetic-scale ion acoustic waves.