Nature of the ring current in Saturn's dayside magnetosphere

We employ magnetic field and plasma particle data from two equatorial passes of the Cassini spacecraft spanning the radial range between similar to 3 and similar to 20 R-S to investigate the nature of the ring current in Saturn's dayside magnetosphere (R-S is Saturn's equatorial radius, equal to 60,268 km). We examine plasma parameters obtained by Cassini for each pass and compare the azimuthal current density profiles deduced with those obtained from current disk modeling of the magnetic field perturbations. We show that the current associated with the P-perpendicular to > P-parallel to pressure anisotropy of the warm water group ions is important inside similar to 10 R-S, canceling a significant fraction of the otherwise dominant inertia current inside similar to 6 R-S. The overall total current density profile is then found to be similar to that produced by the pressure gradient current but augmented in strength by factors of similar to 1.5-2.0 by the difference between the inertia and anisotropy currents. The total current density rises from small values near similar to 6 R-S, peaks at similar to 100 pA m(-2) near similar to 8 R-S, and reduces to values below similar to 25 pA m(-2) at distances beyond similar to 15 RS, up to the 20 R-S limit of our study. The deduced current density profiles are in good agreement with the gross features of the profiles deduced from current disk modeling, with peak values occurring just outside the inner edge of the best fit models at similar to 7 R-S, though with the current density then falling more steeply with radial distance than the 1/r dependence assumed in the model.