Terrestrial versus Jovian VLF chorus; A comparative study

The relevant parameters of the magnetospheres of Jupiter and earth are studied from the point of view of wave‐particle resonant interactions that are believed to be responsible for the generation of VLF chorus emissions observed on Voyager‐1. Using existing models of the cold and energetic plasma distributions in the Jovian magnetosphere, expressions for the wave‐particle interaction length (LI) and the nonlinearity parameter (ρ) are derived. Values of these parameters are compared with those computed for the earth's magnetosphere. It is found that the typical interaction lengths are at least 2–5 times larger in the Jovian than in the terrestrial magnetosphere. Also, the wave intensity necessary to reach the threshold of nonlinearity in the Jovian magnetosphere was found to be up to 5–100 times lower. The Voyager 1 measurements show, however, that the inferred wave magnetic field intensities of the Jovian chorus are in the range of reported intensities for terrestrial chorus. This is attributed to fact that the fluxes of few keV resonant particles found in the Jovian magnetosphere were typically two orders of magnitude higher. In this case, it is predicted that the temporal growth rates of Jovian chorus bursts should be higher than for the earth. Growth rate measurements on Voyager 1 broadband wave data are used to confirm this hypothesis.