Saturn's Magnetospheric Engine: The Mass Loading Cycle

LEISNER, J. S.; RUSSELL, C. T.; KHURANA, K. K.; BLANCO-CANO, X.; STRANGEWAY, R. J.; ARRIDGE, C. S.; BERTUCCI, C.; DOUGHERTY, M. K.

Congreso; American Astronomical Society, DPS meeting #37; 2005

Ion cyclotron waves are nearly ubiquitous in the quiescent E-ring torus from about 4 to 6 Rs. These waves signal strong massloading that enhances the corotating plasma density until the centrifugal force overcomes the drag of the ionosphere and the plasma laden flux tubes move inexorably outward. The strength of these waves is diagnostic of the loss rate of the E-ring exosphere. The newly created ions become sufficiently unstable when the ion perpendicular velocity exceeds about 25 km/s, a pick-up velocity achieved about 4 Rs. Two frequency bands are observed: one beginning at the water-group ion gyrofrequency and a much weaker band beginning about the O2 gyro frequency. The intensity of the ion cyclotron waves varies greatly and occasionally falls below the detectability limit. We interpret this variability as due in part to variations in the neutral exosphere of the E ring that provides the source of the picked-up ions.