Non-stationarity, ion reflection, and wave-particle interactions at quasi-perpendicular shocks

Quasi-perpendicular collisionless shocks are fundamental structures in space plasmas, where the absence of collisions necessitates electromagnetic fields to mediate energy dissipation and particle dynamics. The Magnetospheric Multiscale (MMS) mission, with its high-resolution measurements and multi-point capabilities, provides unique insights into these complex processes. We present MMS observations of ion reflection, electron and ion heating, non-stationarity, wave-particle interactions at quasi-perpendicular shocks. Ion reflection is observed as a critical mechanism for energy transfer, contributing to downstream heating and the generation of instabilities. Non-stationary shock structures, such as ripples and reformation, are identified, showcasing dynamic variations in shock parameters over short spatial and temporal scales. Wave-particle interactions are examined in detail, revealing the role of reflected and minor ions in driving electrostatic and electromagnetic wave activity near the shock front. The observations highlight the interplay between reflected ions and wave generation, which collectively govern shock dynamics and determine the downstream plasma properties. We discuss the need for the novel fields and particle measurements to be provided by Plasma Observatory in order to address the remaining open questions in the field.