SKR variable periods: investigation of north/south fluctuations from short to long-term time scales

Among the persistent questions raised by the existence of a rotational modulation of the Saturn Kilometric Radiation (SKR), the origin of the variability of the ~10.8h SKR period at a 1% level over weeks to years remains intriguing. While its short-term fluctuations (20-25 days) have been related to the variations of the solar wind speed (while the SKR intensity is correlated to the solar wind dynamic pressure), its long-term fluctuations (months to years) were proposed to be triggered by Enceladus mass-loading and/or seasonal variations. This situation has become even more complicated since the recent identification of two separated periods at 10.8h and 10.6h, each varying with time, characteristic of SKR sources located in southern and northern hemispheres respectively. Here, we investigate Cassini Radio Plasma and Wave Science (RPWS) measurements from 1st January of 2004 to the end of 2009. We distinguish both northern and southern SKR components thanks to their circular polarization degree (whose sign is changing with hemisphere) computed from a goniopolarimetric analysis. We then derive SKR northern and southern periods independently, and investigate similarities and differences in their variation at all time scales, in particular below and after the equinox of august 2009, expected to restore a symmetry in SKR generation conditions prevailing in both hemispheres.