Abstract
AbstractWe examine planetary period oscillations (PPOs) observed in Saturn's magnetospheric magnetic field data from the time of Saturn's equinox in 2009. In particular, we focus on the time period commencing February 2011, when the oscillations started to display sudden and unexpected changes in behavior at ~100–200 day intervals. These were characterized by large simultaneous changes in the amplitude of the northern and southern PPO systems, together with small changes in period and jumps in phase. Nine significant abrupt changes have been observed in the postequinox interval to date, commencing as the Sun started to emerge from a long extended solar minimum. We perform a statistical study to determine whether these modulations in PPO behavior were associated with changes in the solar and/or upstream solar wind conditions. We report that the upstream solar wind conditions show elevated values of solar wind dynamic pressure and density around the time of PPO behavioral transitions, as opposed to before and after these times. We suggest that abrupt changes in PPO behavior may be related to significant changes in the size of the Saturnian magnetosphere in response to varying solar wind conditions.
Highlights
Saturn is the only planet within our solar system that has, at least by all measurements to date, a near-perfectly axisymmetric magnetic field [e.g., Burton et al, 2010]
In this paper we have studied abrupt changes in the behavior of the planetary period oscillations (PPOs) identified in the postequinox interval
We have presented evidence that the amplitudes and periods of the PPOs are, at least in part, controlled by conditions external to the Saturnian system by demonstrating that the sharp change in their characteristics appears to be associated with abrupt variations in the size of the Saturian magnetosphere associated with the arrival of interplanetary shocks at Saturn’s magnetosphere
Summary
Saturn is the only planet within our solar system that has, at least by all measurements to date, a near-perfectly axisymmetric magnetic field [e.g., Burton et al, 2010]. It is worth noting that such fluctuation in SKR emissions will be associated with the occurrence of Saturn “auroral storms.” These storms have been reported by Meredith et al [2014] to have a typical cadence of ~5 days, occurring more frequently than the changes in behavior of the PPOs. As mentioned above, Zarka et al [2007] reported fluctuations in the SKR period with a characteristic timescale of 20–30 days associated with variations in the solar wind velocity.
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