Evidence for the occurrence of ~10.6h magnetic field oscillations in Saturn’s equatorial magnetosphere

G. Provan1, D.J. Andrews1, S.W.H. Cowley1, M. K. Dougherty1 and L. Lamy2,3
(1) Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, UK
(2) LESIA, Observatoire de Paris, UPMC, CNRS, Université Paris Diderot, Meudon, France.
(3) Blackett Laboratory, Imperial College London, London SW7 2BZ, UK.

Abstract.

Andrews et al. [2008] and Provan et al. [2009] reported Cassini observations of near-planetary period magnetic field oscillations in Saturn’s near-equatorial magnetosphere, and showed that their period was closely similar to the slowly-varying period of ~10.8 h determined by Kurth et al. [2008] from modulations of SKR radio emissions. Kurth et al. [2008] further reported that these emissions also exhibited a second period of ~10.6 h. Further investigation by Gurnett et al. [2009] revealed that the ~10.6 h modulated emission originates from the Northern hemisphere, whilst the ~10.8 h modulated emission originates from the Southern hemisphere. Andrews et al. [2008] and Provan et al. [2009] also found significant ‘jitter’ in the phases of the equatorial oscillations, and presented evidence that much of this is not due to measurement errors but has a real physical cause. Here we show that this phase ‘jitter’ is due to the superposition in the equatorial magnetosphere of field oscillations at the Southern period with weaker oscillations at the Northern period. We determine the relative amplitudes of these oscillations, and the phase of the Northern period oscillations relative to the Northern SKR modulation.