Azimuthal plasma flow in the Kronian magnetosphere

Abstract

We study the azimuthal plasma velocity in Saturn's magnetosphere between 3 and 13 Saturn radii (Rs) by analyzing energetic particle injection events using data of the Magnetospheric Imaging Instrument (MIMI) onboard the Cassini spacecraft in orbit around Saturn. Due to the magnetic drifts, the injected particles at various energies begin to disperse and leave an imprint in the electron as well as in the ion energy spectrograms of the MIMI instrument. The shape of these profiles strongly depends on the azimuthal velocity distribution of the magnetospheric plasma and the age of the injection event. Comparison of theoretically computed dispersion profiles with observed ones enables us to characterize the azimuthal flow of the plasma. The measured flow profile clearly shows that the plasma subcorotates with velocities as low as 80% of full corotation at radial distances between 8 Rs to 13 R s. With knowledge of the flow profile and the ages of each injection event we can calculate the location where the energetic particles were injected into the inner magnetosphere. The night and morning sector of the Kronian magnetosphere are preferred regions for the generation of hot plasma injections. Copyright 2010 by the American Geophysical Union.