The Polar Cap Boundary of Saturn’s Magnetosphere from Cassini’s High-Latitude Orbits

This thesis is concerned with the structure and dynamics of the polar cap boundary between open and closed field lines in Saturn’s high-latitude magnetosphere, employing data from the Cassini spacecraft to explore methods of identifying such a boundary. The first systematic investigation of the polar cap boundary is presented through a Cassini multi-instrument assessment of observations in various in situ datasets for all the high-latitude boundary region crossings between 2006 and 2009. The average level of coincidence of the polar cap boundary identified in the various in situ data sets is found to be 0.34° ± 0.05° colatitude. The average location of the boundary in the southern (northern) hemisphere is found to be at 15.6° (13.3°) colatitude. The average colatitude of the polar cap boundary during the 2013 high-latitude Cassini orbits was found to be 15.8° (15.1°) in the southern (northern) hemisphere. The associated dayside PCB in the northern hemisphere (NH) is found to be 10.45°. The position of the southern hemisphere (SH) PCB is suggested to be somewhat ordered by the southern planetary-period oscillation (PPO) phase; however, it cannot account for the boundary’s full latitudinal variability. No clear evidence is found of any ordering of the northern PCB location with the northern PPO phase. Solar wind influence on the PCB is investigated; however, a consistent variation is not seen. Finally, FFT wave analysis of Cassini magnetometer data is shown to provide a new method of observing Saturn’s PCB between open and closed magnetic field lines.