Electrostatic electron and ion cyclotron harmonic waves in Neptune's magnetosphere

Abstract

Voyager 2 observations of electrostatic electron and ion cyclotron waves detected in Neptune's magnetosphere are presented. Both types of emission appear in a frequency band above the electron and ion (proton) cyclotron frequencies, respectively, and are tightly confined to the magnetic equator occurring within a few degrees of it. The electron cyclotron waves are interpreted as electron Bernstein modes including an intense upper hybrid resonance emission excited by an unstable loss cone distribution of low‐density superthermal electrons. The ion cyclotron waves are interpreted as hydrogen Bernstein modes including an intense lower hybrid resonance emission excited by an unstable ring distribution of low‐density pickup N+ ions deriving from the satellite Triton.