Evidence that Interaction with the Spacecraft Plasma Wake Generates Plasma Waves Close to the Electron Cyclotron Frequency in the Near-Sun Solar Wind

Prior observations of the near-Sun solar wind (sunward of 0.25 au) identified frequent, intense plasma waves near the local electron cyclotron frequency (f (ce)), and its harmonics. In this Letter, it is shown that near-f (ce) wave properties are consistent with generation via interaction between the observing spacecraft's ion wake and the ambient plasma and magnetic fields. This result implies that many observed near-f (ce) waves are not intrinsic to the unobstructed solar wind flow, and therefore are unlikely to play a significant role in the dynamic evolution of particle distributions in the solar wind.