Periodic narrowband radio wave emissions and inward plasma transport at Saturnian

The abrupt brightening of an Energetic Neutral Atom (ENA) blob or cloud has been interpreted as plasma injection in the Saturnian magnetosphere (termed ENA injection herein). Morphologically, there appears to be two types of abrupt ENA cloud brightening: (1) the brightening of a large cloud usually seen at distances > 10-12 Rs (Rs = 60,268 km) in the midnight or postmidnight region; (2) the brightening of a smaller cloud usually seen at distances < 10-12 Rs around 21-03 magnetic local time (MLT). Among many radio waves observed at Saturn, type 2 ENA injections correlate best with the 5 kHz narrowband waves. Using Cassini INCA and RPWS data, we examine the periodicities of the type 2 ENA injections and the 5 kHz narrowband emissions as well as their cross-correlations, which have been previously used to measure the lag times or phase differences. Because correlational analysis can only establish linear relationships, we also use mutual information to establish linear and nonlinear relationships. On average, the peak of the 5 kHz narrowband emission lags those of the type 2 ENA injection by about a few minutes to 2 hr. The injection of hot plasma into the inner magnetosphere can lead to temperature anisotropy, which can generate electrostatic upper hybrid waves, which upon encountering the high density gradient at the outer edge of the Enceladus density torus, can mode convert to the Z mode and then to O mode. The 5 kHz narrowband waves commonly propagate in the O mode.