Angular beaming model of Jupiter's decametric radio emissions based on Cassini RPWS data analysis

Abstract

Observations of the low frequency part of Jupiter decameter wavelength (DAM) emissions were made using the Cassini radio and plasma wave science (RPWS) instrument. We have analyzed non‐Io‐DAM occurrence dependence from 4 MHz to 16 MHz based on the System III central meridian longitude (CML) of the Cassini spacecraft and calculated the occurrence probability for each frequency. As a result of this analysis, the two peaks of non‐Io‐B and non‐Io‐A occurrence probability showed a dramatic change in longitude between 9 MHz and 16 MHz. At 16 MHz two peaks of probability occurred at 160° and 240° CML. As the frequency decreases to 9 MHz, the two peaks converged to become one peak near 205° CML at 9 MHz. This peak gradually disappeared below 9 MHz. Based on Jupiter's magnetic VIP4 model, an angular beaming model was made to explain these observational results by taking into account the decreasing cone half‐angle of the emitting cone from 16 MHz down to 9 MHz. We found the active magnetic flux tubes of non‐Io‐B and non‐Io‐A sources are localized at about 180° ± 10° of System III longitude projected on Jupiter's surface.