Modeling radio emission attenuation lanes observed by the Galileo and Cassini spacecraft

The Cassini gravity-assisted flyby of Jupiter provided an opportunity to investigate radio emission attenuation lanes that were previously observed in the Voyager and Galileo data. The Cassini radio and plasma wave science (RPWS) investigation is the most advanced plasma wave instrument to visit the Jovian system, measuring electric fields over the frequency range from 1 Hz to 16 MHz with high spectral and temporal resolution. The narrow attenuation lanes in the hectometric emission vary in frequency with system III longitude. The lanes have been modeled in the past assuming a high-latitude cyclotron maser instability source region with emission that is efficiently scattered when the ray path is nearly tangent to the Io L-shell (Gurnett et al., 1998). In the current study we carried out ray tracing of radio emission for multiple frequencies and source regions in a magnetosphere that includes an Io L-shell filled with plasma. The half-width of the density distribution perpendicular to the magnetic field line and the central plasma density of the Io L-shell were fitting parameters. We have used the joint Galileo/Cassini observations at numerous frequencies and radial distances extending to 140 RJ to place constraints on model parameters. The results confirm the suggestion that wave refraction can produce the attenuation lanes. We have also been able to restrict the range of possible hectometric source regions and plasma parameters associated with the density model of the Io L-shell.