A sustained dipolar magnetic field between the current sheet outer edge and the magnetopause, known as a cushion region, has yet to be observed at Saturn. Whilst some signatures of reconnection occurring in the dayside magnetodisc have been identified, the presence of this large-scale structure has not been seen. Using the complete Cassini magnetometer data, the first evidence of a cushion region forming at Saturn is shown. Only five potential examples of a sustained cushion are found, revealing this phenomenon to be rare. This feature more commonly occurs at dusk compared to dawn, where it is found at Jupiter. It is suggested that due to greater heating and expansion of the field through the afternoon sector the disc is more unstable in this region. We show that magnetodisc breakdown is more likely to occur within the magnetosphere of Jupiter compared to Saturn.

The spatial and time characterisation of trapped charged particle trajectories in magnetospheres has been extensively studied using dipole magnetic field structures. Such studies have allowed the calculation of spatial quantities such as equatorial loss cone size as a function of radial distance, the location of the mirror points along particular field lines (’L shells’) as a function of the particle’s equatorial pitch angle, and time quantities such as the bounce period and drift period as a function of the radial distance and the particle’s pitch angle at the equator. In this study, we present analogous calculations for the ‘disc-like’ field structure associated with the giant rotation-dominated magnetosphere of Jupiter as described by the UCL/Achilleos-Guio-Arridge (UCL/AGA) magnetodisc model. We discuss the effect of the magnetodisc field on various particle parameters, and make a comparison with the analogous motion in a dipole field.