Excitation of Saturnian ECH Waves Within Remote Plasma Injections: Cassini Observations

Abstract

Based on Cassini observations, we report representative electrostatic electron cyclotron harmonic (ECH) wave events observed in Saturn's magnetosphere within remote plasma injections. Unlike local injections, remote injections are “older” injection events that have evolved to form a dispersed signature in particle energy spectrum. We show that Saturnian ECH waves within remote injections present a strong fundamental band and much weaker high harmonic bands. By calculating the linear wave growth rates based on the measured electron velocity distributions, we indicate that Saturnian ECH waves can be excited by the loss cone distribution of remotely injected, hot electrons of ∼100 eV to several keV. We find that ECH waves tend to intensify with increased fluxes of injected hot electrons but weakening with increased evolution time of the flux tubes, which is consistent with the results of wave growth rates and improves the current understanding of the generation of ECH waves at Saturn.