Observations of chorus at Saturn using the Cassini Radio and Plasma Wave Science instrument

Abstract

Observations at Saturn of whistler mode chorus emissions have been obtained by the Cassini Radio and Plasma Wave Science instrument. Data from the first 45 orbits are analyzed, and the characteristics of the chorus emissions are discussed. Wave normal and Poynting vector measurements from the five‐channel waveform receiver are used to examine the propagation characteristics of the chorus, and high‐resolution measurements from the wideband receiver are used to examine the fine structure. At Saturn, two different types of chorus are detected. The most common observations are of chorus propagating away from Saturn's magnetic equator, suggesting a source near the magnetic equator. This chorus is usually detected for many hours, is only observed below half the electron cyclotron frequency, and occurs primarily from L shells of about 5 to 8, and the occurrence of the emission shows no obvious correlation with Saturn magnetic latitude, longitude, or local time. The high‐resolution measurements show that the fine structure of this chorus typically consists of larger time scale features (many seconds to minutes) than detected at the Earth (<1 s). The second region of chorus detected at Saturn is in association with local plasma injections. For many of the plasma injection events, chorus emissions are detected both above and below half the electron cyclotron frequency, with a gap in the emission at half the cyclotron frequency. This chorus also shows fine structure at smaller time scales (<1 s to a few seconds), and the overall structure of this chorus appears more similar to chorus detected at the Earth.