Magnetospheric Period Oscillations of Saturn’s Magnetopause and Bow Shock

In this thesis we show that Saturn’s magnetopause and bow shock oscillate with a period near that of planetary rotation that we term the ‘magnetospheric period’. In our first study, using two Cassini orbits as exemplars, we demonstrate that Saturn’s magnetopause oscillates at the magnetospheric period in response to changes in the magnetospheric pressure. The change in internal pressure required to produce such oscillations, which typically correspond to a ~10% change in the boundary radius, is estimated to be ~30-40% of the unperturbed background pressure. In our second study we develop a simple theoretical model of motion through an oscillating planar boundary that is equally applicable to the magnetopause and the bow shock. In our third study we use data from ~40 Cassini orbits to conduct a first systematic investigation of the magnetospheric period magnetopause oscillations. We show that boundary oscillation events are highly organized by the phase of the magnetic oscillations in the ‘core’ region of the magnetosphere. When radial propagation is accounted for, the phase of maximum outward boundary displacement is found to be directly related to the phase of the density maximum in the Enceladus torus. The boundary oscillation amplitude is estimated to be ~1.2 Saturn radii, but is occasionally as great as ~4-5 Saturn radii. In our fourth study we use data from 35 Cassini orbits that crossed both the magnetopause and the bow shock to provide first evidence for magnetospheric period bow shock oscillations. We find that the oscillations are significantly organized by the phase of the ‘core’ magnetosphere magnetic oscillations, though the degree of organization is less than for the magnetopause. The bow shock and magnetopause are found to oscillate approximately in phase within a phase uncertainty of about ± 25° and to have similar oscillation amplitudes.