On the Search for a Generation Mechanism for the Ion Acoustic Waves Observed by the Parker Solar Probe

Abstract

The solar wind plasma is strongly accelerated near the Sun—this acceleration and heating remain beyond 1 au, which contradicts cooling by adiabatic expansion. Wave–particle interaction has been recognized as one of the key mechanisms for particle acceleration and heating in the solar wind. In this context, it is relevant to analyze the origin of the ion acoustic waves (IAWs) observed by the Parker Solar Probe (PSP) and their possible role in solar wind acceleration and heating. PSP has recorded various phenomena during its close encounters with the Sun, including IAWs, current sheets, ion velocity streams, and reconnection exhausts. The origin of the observed IAWs remains unknown. This study investigates the temporal correlation between IAWs, current sheets, ion speed streams, and reconnection exhausts as possible sources of ion beams. Our analysis reveals that current sheets and ion speed streams exhibit a statistically significant temporal proximity with IAWs and also between them, while reconnection exhausts did not show a statistical association with IAWs. These results suggest that current sheets may be associated with proton beams, which then excite IAWs.