Short periodicities in low‐frequency plasma waves at Saturn

Abstract

AbstractShort‐period amplitude modulations (~60 min period) have been detected in the ~100 Hz plasma wave emissions observed by the Radio Plasma Wave Science instrument on the Cassini spacecraft in orbit around Saturn. These periodicities were detected throughout the mission from mid‐2004 to the present, and this is the first statistical study of them. The modulations are observed throughout the magnetosphere and can last from ~2 h to ~20 h, although the duration may be biased by spacecraft observing conditions. The periodicities are statistically much more likely to be seen at high latitudes, both north and south, and at local times between dusk and midnight. When corrected for latitude and local time, the occurrence frequency has declined in time since 2005. Considering all observations, the mean period of these events is 65.3 ± 20.7 min, with a peak (modal value) at 63.3 min. The period has no dependence on local time or latitude. Alfvén waves have interhemispheric transit times commensurate with the mean periods and should thus be considered principal candidates for their production.