Planetary period oscillations in Saturn's magnetosphere: Examining the relationship between abrupt changes in behavior and solar wind‐induced magnetospheric compressions and expansions

Abstract

We 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.

An SLS5 Longitude System Based on the Rotational Modulation of Saturn Radio Emissions

“…However, the two periods crossed each other briefly in late 2009 and started to oscillate around 10.7 hr for four years after equinox (Fischer et al, , ), before the northern hemisphere finally slowed down toward the end of mission (Ye et al, ). Similar developments were also observed in magnetic field perturbations (Andrews et al, ; Cowley & Provan, ; Provan et al, ; Provan et al, ).…”

Energetic Electron Periodicities During the Cassini Grand Finale

“…The period is not constant but rather changes by ~1% over intervals of a year or longer (Galopeau & Lecacheux, ; Gurnett et al, ). Changes in the period are observed in radio emissions (Kurth et al, 2008, 2007; Lamy, ), magnetic fields (Provan et al, , , ), and charged particles (Carbary & Mitchell, 2017; Carbary et al, ). Second, the periodicities themselves are divided into a northern branch and a southern branch, which may have slightly different periods (Andrews et al, ; Carbary et al, ; Gurnett, Lecacheux, et al, ; Gurnett, Persoon, et al, ).…”

Swept Forward Magnetic Field Variability in High‐Latitude Regions of Saturn's Magnetosphere

“…Distinguishing the influence of these systems on phenomena becomes easier during times wherein their modulation periods are most separate. Fortunately for this work, early 2008 represents such a time (see, for example, Provan et al, , Figure 2), with the northern and southern periods being separated by approximately 0.2 h.…”