Comparison between Cassini and Voyager observations of Jupiter's decametric and hectometric radio emissions

Abstract

[1] In this paper, we attempt to clarify the relationship between Jovian hectometric (HOM) and non-Io-related decametric (non-Io-DAM) radio structure. For that purpose, we extend the analysis by including more data and investigating statistical properties of the Jovian DAM and HOM radio emissions based on Cassini and Voyager observations, especially below 16 MHz. We have investigated these emissions observed by the Cassini, Voyager 1, and Voyager 2 spacecraft for specific Jovigraphic latitudes in the range of −3.7°–7.3° and local times in the range of 0.76–21.4 hours. We show a statistical comparison of Cassini, Voyager 1, and Voyager 2 data for occurrence probability in Central Meridian Longitude (CML) versus Io phase and in CML versus Frequency. The main results are as follows: (1) the detailed frequency structures of non-Io-related components can be seen for different spacecraft's local time and Jovigraphic latitude, (2) the high frequency of HOM extends up to near 10 MHz, and (3) a new DAM component, named the non-Io-D, appears from 40° to 60° CML in the frequency range of 7–11 MHz. On the basis of additional information of different behaviors of non-Io-B and non-Io-A structures in longitude depending on pre- and post-encounter of Cassini data, we improved the DAM angular beaming model that shows the cone half-angle of the emitting cone decreases as a function of frequency. We conclude that the changing beaming angle is not affected by Jovigraphic latitude of the spacecraft, but rather due to different local time of the source regions.