Sources of rotational signals in Saturn's magnetosphere

Abstract

Saturn's internal magnetic field is exceptionally symmetric about its rotation axis. Yet local and remotely sensed observations of field and plasma in Saturn's magnetosphere display periodicities close to Saturn's rotation period. In this communication we provide evidence that Saturn's inner/middle magnetosphere contains semipermanent azimuthal anomalies in the ring current region in the fluxes of energetic charged particles, plasma density, magnetic field, and electrical current with a longitudinal wave number m = 1. We demonstrate that in the presence of these anomalies and a finite solar elevation angle, the solar wind lifts Saturn's magnetosphere asymmetrically in longitude, generating a tilt in the current sheet of Saturn. The current sheet tilt further produces periodicities in Saturn's middle and outer magnetosphere. The ubiquitous nature of the ring current region anomalies and their profound influence on the magnetospheric structure strongly suggest that the period of the Saturn kilometric radiation (SKR) wave power is controlled by them.