The Contribution of Planetary Period Oscillations towards Magnetic Reconnection at Saturn

Abstract:

Magnetic reconnection occurs through topological reconfiguration of the magnetic field within a current sheet. It has been shown to be a key driver of particle acceleration in Saturn's magnetosphere, and is crucial for the removal of plasma from the system. Two primary drivers of this process have been identified at Saturn: the solar wind, and the rapidly rotating internally generated Enceladus plasma torus. The aim of this study is to investigate the contribution of a possible third driver of reconnection at Saturn known as Planetary Period Oscillations (PPO). PPOs refer to the ~10.6 hour periodic modulation phenomenon observed in all magnetospheric datasets at Saturn. These periodic oscillations are driven by two rotating field-aligned current systems, one in each hemisphere, which combine to perturb the equatorial current sheet and magnetic field.

Observations have shown that PPOs periodically modulate the thickness and position of the equatorial current sheet, depending on the relative phase and amplitude between the northern and the southern PPO systems. Using an empirical model presented by Cowley et al. 2017, we investigate the amplitude of the PPO systems required to modulate the current sheet half-thickness to within the characteristic length scales favourable for the onset of magnetic reconnection. We constrain the amplitude of the PPO systems from empirically determined current sheet half-thickness values from Cassini data and discuss if the influence of PPOs are sufficient to trigger reconnection alone, or require conjunction with the other drivers. Finally, we present theoretical estimates of the reconnection rate and energy release associated with such PPO driven reconnection events, assuming sufficiently strong PPO systems.