Saturn's ring current: Local time dependence and temporal variability

Abstract

Radial profiles of the azimuthal current density between similar to 3 and 20 R-S in Saturn's magnetosphere have been derived using plasma and magnetic field data from 11 near-equatorial Cassini orbits spanning a 10 month interval. The current density generally shows only modest variations with local time and from pass to pass within this region, rising rapidly near similar to 5 R-S to peak at similar to 90 pAm(-2) at similar to 9 R-S and falling more gradually to below similar to 20 pA m(-2) at 20 R-S. The pressure gradient current is overall the most important component, the dominant inertia current in the inner region being significantly canceled by the oppositely directed pressure anisotropy current. These characteristics principally reflect the properties of the warm water plasma originating from the Enceladus torus to distances of similar to 10 R-S encompassing the usual current peak, inside of which distance the plasma properties are generally unvarying within factors of less than similar to 2. Increased variability is present at larger distances where the pressure of the hot magnetospheric plasma plays the more important role. In this region the dominant pressure gradient current is found to be strongest in the dusk to midnight sector and declines modestly, by factors of similar to 2 or less, in the midnight to dawn and dawn to noon sectors. Pass-to-pass temporal variability by factors of similar to 2-3 is also present in the outer region, particularly in the dawn to noon sector, probably reflecting both hot plasma injection events as well as solar wind-induced variations.