Morphology of Interchange-Driven Injections in Saturn’s Magnetosphere

As Cassini passes close to Saturn during its regular orbits, evidence of particle injections can often be found in many different data sets (including MAG, CAPS, MIMI, and RPWS). One reason injections are easily visible in Saturn’s inner magnetosphere is that the circumplanetary neutral gas distribution can reduce the intensities of some charged particles. For example, energetic ions can be lost from the system following charge exchange with neutrals and energetic electrons can lose energy in collisions with gas and dust. Injections in the inner magnetosphere are believed to be flux tube interchange events that are part of a larger circulation system in which cold dense plasma flows outward carrying magnetic flux with it. The closed magnetic flux is ultimately returned to the inner magnetosphere in the form of injections of rapidly moving hotter but lighter flux tubes from the middle magnetosphere. In this presentation, we will look at injections from the perspective of multiple Cassini data sets. Some features of these structures have already been identified in the literature from one or more data sets. For example, the tendency for injections to appear as enhancements (depressions) in magnetic field strength at low (high) magnetic latitude has been documented (Andre et al. 2007). Furthermore, that flux tube bundles seem to narrow in spatial extent in the equatorial plane in the higher magnetic field region has also been described. Here, we will look at selected structures distributed in radial distance and latitude as a step toward generalizing their characteristics at various locations. We will consider issues such as the magnetic signature in the field components, the typical wave signatures, the energy range of the injection, and the presence of isolated features versus multiple features occurring simultaneously. We will also discuss observational issues, such as when each instrument is optimally suited to detect injections, and how this relates to their structure.

Andre, N., et al. (2007), Magnetic signatures of plasma-depleted flux tubes in the Saturnian inner magnetosphere, Geophys. Res. Lett., 34, L14108.