The proton concentration in the vicinity of the Io plasma torus

Abstract

This paper uses an improved model for the plasma distribution in Jupiter's magnetosphere to determine the light ion concentration in the vicinity of the Io plasma torus from whistler dispersion measurements. The model used assumes that the plasma is in diffusive equilibrium under the action of centrifugal, gravitational, and ambipolar electric field forces. The study provides an estimate of the plasma concentration at intermediate and high latitudes along field lines through the Io plasma torus. The method employed is to combine the Voyager 1 plasma wave instrument whistler observations with the Voyager 1 plasma instrument heavy ion charge concentrations throughout the Io torus to determine the light ion charge concentration along the whistler propagation paths. Because the light ion source is probably Jupiter's ionosphere and because Jupiter's atmosphere is primarily hydrogen, the light ions are taken to be protons. Whistlers at 13 L values between L = 5.25 and L = 5.85 are analyzed. Values of NL², the total number of ions per unit L multipled by L², are calculated and the ratio NL² (protons)/NL² (electrons) is found to have an average value of 0.2. This ratio is used to give a rough estimate for the ionospheric source strength.