Ordering of injection events within Saturnian SLS longitude and local time

Abstract

Periodicities similar to the Saturn kilometric radio (SKR) emissions have been observed throughout the magnetosphere in both the magnetic field and the plasma. An outstanding question is what mechanism links these periodicities between the inner and outer magnetospheres. It had been postulated that the interchange instability, where narrow injections return the magnetic flux carried by the bulk plasma outflow, could play a role in determining the periodicities, but early analysis found no ordering of the injection events in the SKR-derived Saturnian longitude system (SLS). In this study, we reexamine this possibility by limiting our data set to the young injection events observed by the Cassini radio and plasma wave science instrument. We find that the young injection events observed near midnight local time are strongly ordered by SLS. Further, this ordering varies with the Saturnian season. Pre-equinox, the northern hemisphere's longitude system controls the event occurrence. Post-equinox, the events are ordered by the southern hemisphere-derived longitude system. We suggest that this may be an effect in the variations in ionospheric conductivity or due to change in the magnetosphere's orientation relative to the solar wind. © 2013 American Geophysical Union. All Rights Reserved.