Evidence of fresh injections related to the interchange instability in the Io torus

The Juno Waves instrument often detects brief, band-limited emissions when the spacecraft crosses magnetic fields threading Io's M-shell, or vicinity thereof, up to about 35 degrees magnetic latitude. The disturbances have durations of order one minute and are observed below the electron cyclotron frequency. While plasma densities are often not available, it is thought that the frequency of the events are below the plasma frequency of the surrounding medium. Often, the first electron cyclotron half-harmonic is weakened or disrupted at the time of the events. While the events can be seen in isolation, there are typically a few of them with temporal spacing from about 15 to 40 minutes. In this paper we suggest that the events observed by Juno are signatures of injections. Injections have been reported in the Io torus or its vicinity dating back to the Galileo mission. However, the events reported here are somewhat different in that most exhibit little or no variation in magnetic field strength and due to the radiation environment, we have minimal plasma measurements with which to compare. We show that the locations of these events are on field lines threading the dense Io torus, with several inside of Io's M-shell. We discuss reasons to believe these events are the same or similar to the earlier reported injections.