Periodicities Related to Saturn’s Magnetospheric Dynamics

Document Type

Article

Publication Date

12-9-2024

Abstract

Saturn's magnetosphere exhibits periodicities ranging from minutes to days. A comprehensive understanding of the various physical drivers, their characteristic periods, and their potential interconnectedness is lacking. The shortest time scales have been attributed to field line resonances (FLR), which includes Saturn's ubiquitous quasi-period of 60 minutes (QP60). However, more recent studies have suggested that Kelvin-Helmholtz (KH) vortices on the magnetopause boundary have a characteristic time scale on the order of one to four hours; therefore, KH could also contribute to QP60. Substantial interest has also been generated by Saturn's Planetary Period Oscillation (PPO) which is thought to be related to the planet's rotation period (~10.7 hours), sourced in the ionosphere/atmosphere. However, there is also significant periodic behavior at longer timescales, ranging from >11 hours to days. We suggest that subcorotational periodicities are related to magnetospheric dynamics, presenting a key diagnostic of mass loss processes and magnetic flux circulation time scales. We use a continuous wavelet transform (CWT) analysis of Cassini magnetic field (MAG) and density fluctuations (CAPS/ELS) for an ensemble of orbits in the midnight sector and dawn/dusk flank regions to quantify Saturn's non-PPO periodicities. Comparison with equivalent time series taken from Grid Agnostic MHD for Extended Research Applications (GAMERA) simulations will be made to determine the possible contributions from KH waves on the magnetopause boundary and periodic plasmoid formation in the tail under steady solar wind conditions. We will analyze the simulation results with information theory to determine linear and non-linear relations, giving clues to the source mechanisms for periodic behavior.

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