Understanding the global evolution of Saturn's ring current

An explanation for the morphology and evolution of the ring current in Saturn's magnetosphere is provided. We use global Energetic Neutral Atom (ENA) images of the 20-140 keV proton distribution obtained by the Ion and Neutral Camera (INCA) on board the Cassini spacecraft. A case where the ring current displays an exceptionally clear spiral shape is analyzed and by using a simple model of rotational velocities and curvature-gradient drifts we reproduce the observed spiral patterns and dispersions. The spiral evolve from an initial large-scale injection around midnight consistent with INCA observations. The drift patterns of the inner magnetosphere have to be relatively undisturbed in order for a clear spiral to evolve. Clear spiral patterns like this do not always occur, which reminds us that the inner magnetosphere of Saturn is indeed very dynamic.