Electrostatic Waves at a Quasi‐Parallel and a Quasi‐Perpendicular Interplanetary Shock

We present analysis of broadband electrostatic fluctuations observed on the Magnetospheric Multiscale satellite around the ramp of one quasi‐parallel and one quasi‐perpendicular interplanetary shock. In both shocks, wave packets are shown to be overall similar. They have plasma frame speeds mostly less than 200 km/s, comparable with the ion‐acoustic speed, wavelengths of 100–500 m or 10–50 Debye lengths, and electrostatic potential amplitudes mostly within 0.01–0.3 V or 0.1%–1% of the local electron temperature. Most wave packets are polarized nearly parallel to the local magnetic field, though nearly perpendicular polarizations also occur in both shocks. Based on the revealed parameters, we interpret the electrostatic fluctuations as ion‐acoustic waves. The revealed wave properties are compared with those reported at Earth's bow shock and potential sources of this wave activity are discussed.