Observation of Periodic Rising and Falling Tone ECH Waves at Saturn

Abstract

Electron cyclotron harmonic (ECH) waves are effective in precipitating electrons into the loss cone to form diffuse aurora. Recent observations have shown that ECH waves at Earth could exhibit frequency chirping, which is an interesting feature of various plasma waves and whose mechanism is under intensive research. Whether chirping of ECH waves is also present in other planetary magnetospheres, however, is unknown. In this paper, we report the first observation of quasi-periodic ECH waves with frequency chirping at Saturn using Cassini data. The identified six falling tone and one rising tone ECH wave events occur at (Formula presented.) near the magnetic equator. The duration of ECH wave chirping elements lasts from seconds to minutes. Our findings suggest that frequency chirping of ECH waves could be observed at other planetary magnetosphere, and are useful to understand the fundamental mechanisms of frequency chirping of various plasma waves.