Saturn's Planetary Period Oscillations During the Closest Approach of Cassini's Ring-Grazing Orbits

Abstract

Saturn's planetary period oscillations (PPOs) are ubiquitous throughout its magnetosphere. We investigate the PPO's azimuthal magnetic field amplitude interior to the field-aligned currents, during the closest approaches of Cassini's ring-grazing orbits (October 2016 to April 2017), with periapses at 2.5 R_S. The amplitudes of the northern and southern PPO systems are shown to vary as a function of latitude. The amplitude ratio between the two PPO systems shows that the northern system is dominant by a factor of 1.3 in the equatorial plane, and it is dominant to -15° latitude in the southern hemisphere. The dayside amplitudes are approximately half of the 2008 nightside amplitudes, which agree with previous local time-related amplitude observations. Overall, there is clear evidence that the PPOs are present on field lines that map to the outer edge of Saturn's rings, closer to Saturn than previously confirmed.