Rotational Modulation of the High Frequency Limit of Saturn Kilometric Radiation.

The high frequency limit (HFL) of the Saturnian Kilometric Radiation (SKR) can probe the deepest SKR sources, closest to Saturn's ionosphere. In this study, we determined and analyzed the SKR HFL throughout the entire Cassini Saturn orbital tour. The maximum frequency of the northern SKR, whose distribution peaks at ~625 kHz, is shifted by +100 to +200 kHz from the distribution of southern SKR HFL, consistent with the magnetic field offset toward the northern hemisphere at Saturn. The uniformly observed SKR HFL in the vicinity of Saturn suggests a broad extent and beaming of the SKR source. When the observer is confined to certain locations, the rotational modulation of the SKR HFL is clearly observed. This modulation feature of the SKR HFL is statistically established and analyzed in this study. The modulation of HFL is best observed at mid-latitudes between 10° and 40° and at almost all local times. We perform a simulation that suggests that the modulation of HFL requires the superposition of a "clock" like and a rotating source behavior. By comparing the derived HFL modulation using different longitudes with variable and fixed rotation periods, we can exclude the existence of a magnetic anomaly that was proposed in a previous study based on the Voyager data. The calculation of the least-square periodogram confirms that the modulation observed in HFL is similar to the ones previously detected at Saturn. [ABSTRACT FROM AUTHOR]