Ion Reflection by a Rippled Perpendicular Shock

We use multi-spacecraft Magnetospheric Multiscale (MMS) observations to investigate electric fields and ion reflection at the ramp of a non-stationary perpendicular shock with $M_A$=6. We identify sub-proton scale (5-10 electron inertial lengths) large-amplitude normal electric field structures primarily balanced by the Hall term ($\mathbf{J} \times \mathbf{B}/ne$). Such electric fields are a transient feature related to the shock non-stationarity (rippling). The corresponding electrostatic potential is comparable to the energy of the incident solar wind ions and thus significantly contributes to ion reflection.