Cold torus whistlers: An indirect probe of the inner Jovian plasmasphere

The dominant features of Jovian whistlers observed by Voyager 1 in the inner cold torus around R J ≈ 5.3 are studied using the technique of ray tracing with an offset tilted dipole. These whistlers are unducted, and the electron density in the inner plasmasphere plays a controlling role in the access of whistlers to the cold torus. The upper frequency cutoff of inner zone whistlers allows a firm limit to be placed on the minimum electron density 3–5 cm −3 at higher latitudes in the inner plasmasphere around L ≈ 5.3, a region where no spacecraft have ever been. Backward ray tracing from the observation location is used to determine the source location at the top of the Jovian atmosphere, and it is shown to be consistent with the latitude of lightning events observed by Voyager 1.