Solar wind electron-streaming instability dynamics with lunar magnetic anomaly

Abstract We analyse the electrostatic modes triggered by the electron-streaming instabilities in the magnetised solar-wind plasmas over the lunar magnetic anomalies (LMAs). A standard normal mode analysis is applied to derive a generalised linear dispersion relation to understand the observed electrostatic modes in the Moon over the LMAs. The various excited wave modes are illustratively identified and characterised. The interaction between the electron-beam mode and the normal acoustic modes, including their branch coupling and coalescence, is examined to elucidate the origin of the electron-streaming instability. We further investigate the effects of the propagation angle (θ) variation, relative to the interplanetary magnetic field (IMF), on the instability growth rate. The stabilising effects of the IMF on the instability are investigated. The consistency of this analysis in light of the existing Kaguya observations is finally established.