Extended Survey of Saturn Z-Mode Wave Intensity Through Cassini's Final Orbits

Abstract

Similar to whistler mode chorus, Z-mode emission is an efficient diffusive scatterer of electrons possibly resulting in resonant acceleration. We present results of a survey of both the low-band (5 kHz) and for the first time the high-band (20 kHz) intensity of these emissions, based on over 11 years of Cassini Radio and Plasma Wave Science instrument data including nine ring-grazing orbits and two proximal orbits, which occurred at the end of the mission. We distinguish these emissions using density and polarization measurements and calculate the mean intensity as a function of frequency and spatial coordinates. We find that the average low-band Z-mode intensity peak is P0 ~7 × 10−8 nT2, while the high-band peak is much lower at P0 ~10−9 nT2. The spatial distribution of intensity differs for each emission band implying different source regions and perhaps different source mechanisms.