[1] Plasma data from the Cassini Plasma Spectrometer experiment were used to investigate the properties of the variable plasma environment of Titan's orbit. The characteristics of this plasma environment play a crucial role in the plasma-moon interaction and also have a strong influence on the ionosphere of Titan. Using dynamic energy spectra of ions within ±3 h of the Titan flybys we identified different ambient plasma environments, similar to the ones proposed earlier based on electron measurements. Expanding the time interval to 12 h to cover full SKR periods, and taking into account the composition of the ions, we showed that the longer intervals include all the previous categories, and a special one, a short event, rich in heavy ions. Detailed study of the vicinity of these events revealed the fine structure of the magnetodisk of Saturn, having a narrow central sheet of very high heavy ion content, heavy rich events occurring when the spacecraft crosses this central sheet. We also proved that the heavy rich events appear periodically in longitude, but with a period slightly (by 0.35°/day) longer than the SLS3 period.

[1] We investigate ion densities derived from measurements by the Cassini Plasma Spectrometer, to determine how these ions are distributed around the magnetodisk of Saturn. The magnetodisk is a variable plasma structure, here we fitted the simple structural model of Arridge et al. (2011) as a reference for the location of the central line of the magnetodisk. This study covers the time range DOY 092-285, 2009, around Saturnian equinox, along nine orbits of the Cassini spacecraft, each of which included a Titan flyby. We also investigated the covariance of the magnetic field components during that period of time. Our main findings are: a) The simple structural model of Arridge et al. (2011) agrees well with the thermal ion density observations and works well in the equinox season of Saturn. b) In this data set the locations of the central sheet of the magnetodisk is identified by the change of sign of B R . At those locations we observed higher heavy ion densities and narrower confinement to the equator than those of protons. The heavy ion and proton layers exhibited the same structure that was found during the primary mission. c) The observed flapping amplitudes of the magnetosheet relative to the spacecraft were high, reaching 5 R S . d) The relative phase of the magnetic field components were different in the equatorial regions and in the lobes (>5 R S ).

[1] In this report, we modify the model of Arridge et al. (2011) which was proposed to describe the shape of the magnetodisk of Saturn and its north-south oscillations near the planetary rotation period. The modification is based on the recent results of Provan et al. (2011Provan et al. ( , 2012 and Andrews et al. (2012), who have shown that the magnetic modulations near the current sheet exhibit dual periodicities, and derived magnetic phase functions for the northern and southern period modulations from the magnetic field data. Using a modified model in which the effects of both modulations are included, specifically related to the modulations of the radial component of the magnetic field, we show that the oscillations can be modeled without the use of an arbitrarily assigned oscillation phase value as employed in the previous work of Szego et al. (2012). In addition, the best fit amplitudes of the two oscillations are found to be nearly constant for a majority of the magnetodisk data analyzed, such that a single model with one fixed parameter fits well to the data for a majority of the passes.

[1] We analyze ion densities derived from the data of the Cassini Plasma Spectrometer for the time period of the prime mission till the end of May 2008, in the low latitude outer magnetosphere near Titan encounters. We have found that the central line of the magnetodisk is surrounded by a structured plasma sheet, a smooth, broad ion layer composed of light ions, and a heavy ion layer displaying narrow substructures. The heavy ion densities are spiky; the co-location of the observed enhanced ion plasma densities with the change of sign of the radial component of the magnetic field is demonstrated. At these locations the heavy ion density is the highest. The plasma sheet is denser and wider on the dayside of Saturn than on the nightside; in the lobes the protons were dominant. Based on a statistical analysis for proton densities measured between radial distances from 10 R S to 22 R S we project densities to Titan's orbital distance. We show that the projected proton density in the magnetodisk in organized by SLS3 longitude and, therefore, is modulated by SKR. In the lobes, the proton density is nearly constant. High heavy ion density in the sheet is accompanied by low heavy ion temperature. The magnetospheric interaction with Titan is primarily defined by the SLS3 phase of the encounter and the distance of the moon from the magnetic equator. Accordingly, the incoming plasma flow impinging on Titan cannot be stable for a few hours before the encounter.