Periodic narrowband radio wave emissions and inward plasma transport at Saturnian magnetosphere

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 r > 10-12 Rs (Rs = 60,268 km) in the midnight or postmidnight region; (2) the brightening of a smaller cloud usually seen at r < 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 peaks of the 5 kHz narrowband emission lag those of the type 2 ENA injection by a few minutes to 2 hr.  The injection of hot plasma to the inner magnetosphere can lead to temperature anisotropy, which can lead to the growth of the electrostatic upper hybrid waves, which upon encountering the density gradient at the outer edge of the Enceladus plasma torus, can mode convert to the Z mode and then to O mode.  The 5 kHz narrowband waves commonly propagate in the O mode. It is expected that the same processes can occur in Jovian magnetosphere and hence our study can provide insights into the upcoming observations by JUICE/PEP/JENI and RPWI. The results also have implications to more distant astrophysical objects such as brown dwarfs, which have been observed to emit periodic radio waves.