The electron density of Saturn's magnetosphere

Abstract

Abstract.We have investigated statistically the electron density below 5 cm −3 in the magnetosphere of Saturn (7-80 R S , Saturn radii) using 44 orbits of the floating potential data from the RPWS Langmuir probe (LP) onboard Cassini. The density distribution shows a clear dependence on the distance from the Saturnian rotation axis (as well as on the distance from the equatorial plane (|Z|), indicating a disclike structure. From the characteristics of the density distribution, we have identified three regions: the extension of the plasma disc, the magnetodisc region, and the lobe regions. The plasma disc region is at L <15, where L is the radial distance to the equatorial crossing of the dipole magnetic field line, and confined to |Z| <5 R S . The magnetodisc is located beyond L=15, and its density has a large variability. The variability has quasi-periodic characteristics with a periodicity corresponding to the planetary rotation. For Z > 15 R S , the magnetospheric density distribution becomes constant in Z. However, the density still varies quasi-periodically with the planetary rotation also in this region. In fact, the quasiperiodic variation has been observed all over the magnetosphere beyond L=15. The region above Z=15 R S is identified as the lobe region. We also found that the magnetosphere can occasionally move latitudinally under the control of the density in the magnetosphere and the solar wind. From the empirical distributions of the electron densities obtained in this study, we have constructed an electron density model of the Saturnian nightside magnetosphere beyond 7 R S . The obtained model can well reproduce the observed density distribution, and can thus be useful for magnetospheric modelling studies.Correspondence to: M. W. Morooka (morooka@irfu.se)

The latitudinal structure of the nightside outer magnetosphere of Saturn as revealed by velocity moments of thermal ions

“…The periodicity of these heavy rich events was found to be close to the southern SKR period. Morooka et al (2009) have shown that quasiperiodic variations of the electron density can be observed all over the magnetosphere, even in the lobe region beyond L = 15. They also found that Saturn's magnetosphere has a strong longitudinal asymmetry.…”

The rotation of the plasmapause-like boundary at high latitudes in Saturn's magnetosphere and its relation to the eccentric rotation of the northern and southern auroral ovals

“…[3] Although various particle and field observations in Saturn's magnetosphere showed periods similar to the SKR modulation [Espinosa and Dougherty, 2000;Carbary et al, 2007;Morooka et al, 2009], it was only recently that the northern and southern SKR periods have been identified in other data. In particular, Andrews et al [2010] showed that the north and south SKR periods correspond to the rotation periods of quasi-dipolar magnetic field perturbations observed at high latitudes over the northern and southern polar regions, and Nichols et al [2010] showed that the two SKR periods are the same as the periods of dawn-dusk oscillations of the northern and southern auroral ovals as viewed by the Hubble Space Telescope (HST).…”

The orientation of Titan’s dayside ionosphere and its effects on Titan’s plasma interaction

“…This periodicity can cause a larger variability at Titan than the solar wind (cf. Persoon et al, 2005Persoon et al, , 2006Morooka et al, 2009). Simon et al (2010a) classified the first 62 Titan flybys as lobe-type or current sheet.…”