Generation of Ion-scale Plasma Waves near Shocks Observed by Solar Orbiter

Abstract Plasma waves, turbulence, and shocks are commonly observed in the solar wind. In this study, we investigate the interaction between ion-scale waves and shocks using in situ spacecraft observations. We focus on two possible scenarios: the transmission of waves across shocks, and the local generation of waves through kinetic instabilities. We examine two shock events observed by Solar Orbiter: one at Earth’s bow shock, and the other an interplanetary shock located at approximately 0.5 au. Both events exhibit ion-scale wave activity upstream and downstream of the shocks. Based on the relationship between the upstream and downstream wave frequencies and wavevector magnitudes, we find no clear evidence supporting a simple transmission of ion-scale waves across the shock in these events. By analyzing the observed ion velocity distribution functions, we find that the ion-scale waves near shocks are more likely generated locally by ion-driven kinetic instabilities, in contrast to the behavior of MHD-scale turbulence. These results indicate that local plasma conditions play a dominant role in shaping kinetic-scale waves in the vicinity of shocks.