Origin of Jovian hiss in the extended Io torus

Plasma wave observations on Voyager, Ulysses, and Galileo have shown that whistler-mode hiss at frequencies below one kHz is continuously present in the extended Io torus of Jupiter. Cyclotron resonant energies at frequencies below 1 kHz are extremely high ( typically > MeV), and the Jovian resonant electron flux is too low to cause significant local wave amplification. We consequently explore the possibility that Jovian hiss could be generated elsewhere, and then propagate into the torus to form the observed hiss band. Based on previous studies of the properties and excitation region of Jovian chorus emissions, we demonstrate that whistler-mode waves originating as discrete chorus emissions in the tenuous region from 10 to 15 R-J can refract and propagate inwards into the dense Io torus and there merge into a band of low-frequency hiss. This proposed mechanism for the origin of Jovian hiss is analogous to the formation of plasmaspheric hiss at Earth.