Analytical Modeling of Hot Ion Interchange Injections in Saturn's Magnetosphere

Cassini's CHarge Energy Mass Spectrometer (CHEMS) instrument collected energetic plasma data from 2004 to 2017, including hundreds of observations of small‐scale nearly dispersionless “local” injection events into the inner magnetosphere. This study assesses whether these interchange‐like injections are a channel‐like structure still connected to the outer region or whether they are typically a small, isolated zone that is disconnected from the source location. We model these events with a simple azimuthal drift code, which evolves the injections forward in time around the equatorial plane of Saturn. The results are compared against Cassini observations if their predicted path intersected the Cassini spacecraft again within 0.25 R s (Saturn radii). Our analysis of these events determined that out of the 816 events, only 243 injections intersected Cassini's trajectory again. By examining the CHEMS spectrogram data during these expected intersections, we found that a majority (186 injections, 77%) displayed an energy‐dispersion signature that aligned closely with the modeled dispersion pattern, indicating that the injections are of “channel‐like,” or radially extended (several R S ) morphology. The nominal runs assumed a typical co‐rotation velocity, and while this worked for 93 (50%) of matching events, the other half required a slight adjustment (within 10%). Additionally, 38 events (20%) required a slight adjustment to the magnetic gradient‐curvature drift term. Estimates of this nature advance subsequent calculations of transport of energetic plasma to the inner magnetosphere of Saturn.