Magnetic Polarization and Phase Structure of Saturn's 10.7-Hour Oscillations

Monday, 15 December 2014
Japheth Nesta Yates, David J Southwood and Michele Karen Dougherty, Imperial College London, Blackett Laboratory, London, United Kingdom
A source of Saturn's magnetic 10.7-hour period oscillations has yet to be identified. The oscillations are known to consist of signals with slightly different periods from separate northern and southern sources. Here we present a novel way of examining observations, focusing on signal phase. We show that although the signals are highly periodic they are usually not sinusoidal and that there are differences in both phase structure and polarization between the outer magnetosphere (on the nightside) and the inner dipolar region. Paying particular attention to the deep mid-tail passes of 2006, the contrasting behaviour between the inner and outer regions is clear with approximate sinusoidal behaviour in the dipolar region and a pulse like signal once per cycle in the tail. The latter structure seems to indicate that tail magnetic stress is released impulsively once per cycle in the tail. After equinox, in 2010-11, we find a different picture in the pre-midnight sector. The pre-determined northern and southern frequencies are closer together and apparently show sudden shifts. Our signal reconstruction approach finds instances where it is likely that the narrow band filtering is not able to track completely the basic north and south periods as we find phase jumps indicating unpredicted beats.