Modeling of Saturn kilometric radiation arcs and equatorial shadow zone

Abstract

Accelerated electrons gyrating around Saturn's auroral (high latitude) magnetic field lines generate the intense Saturnian kilometric radiation (SKR). This radio emission is thought to be generated via the cyclotron maser instability (CMI) that predicts a strong anisotropy of the beaming pattern of the emission. Resulting visibility effects were suspected to be at the origin of characteristic features observed in Cassini's dynamic spectra as arc‐shaped structures and shadow zones. By using the Planetary Radio Emissions Simulator (PRES) code, we model these visibility effects and their consequence on Cassini's observations of SKR: we compute the dynamic spectra resulting from the beaming pattern of CMI‐generated SKR and its intersection with Cassini's trajectory. The SKR beaming pattern and its dependence on the frequency is computed for two typical electron distributions observed in auroral regions: a loss cone (favoring oblique emission) or a shell (favoring perpendicular emission). We successfully fit observed arc‐shaped structures and shadow zones. Although oblique and perpendicular emissions both allow to produce radio arcs, the fit is better in the oblique case. Similarities and differences between observations and model results are discussed and perspectives are outlined.