The Role of Electron Density on the Interchange Instability at Saturn

Interchange events, where “injections” of hotter, less dense plasma moves inward to return the magnetic flux carried outward by the colder, more dense plasma in rapidly rotating magnetospheres, are detected at Saturn by Cassini on almost every orbit that encounters the inner and middle (<15 Rs) magnetosphere. Significant changes can occur in the number of injection events and their location (L shell) between inbound and outbound passes on a given orbit (over a several hour time span). Furthermore, changes are observed between orbits for the same local time sampling (over tens of days). Similar changes between inbound and outbound passes, and between orbits have been observed in the electron density values measured by Cassini. We examine the period in 2010 when Cassini was in near equatorial orbits with the inbound period between L of 4.5 and 10 primarily in the midnight sector and the outbound period was near noon. Using Cassini Plasma Spectrometer (CAPS) and Magnetospheric Imaging Instrument (MIMI) data we determine the occurrence of injection events, their signature in a wide range of energies (eV to MeV), and examine their relationship with the electron density determined from the upper hybrid resonance emission measured by the Radio and Plasma Wave Science instrument.