Physics
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsm41b..05b&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #SM41B-05
Physics
2720 Energetic Particles: Trapped, 2730 Magnetosphere: Inner, 2740 Magnetospheric Configuration And Dynamics, 2756 Planetary Magnetospheres (5443, 5737, 6033), 2778 Ring Current
Scientific paper
Energy dispersion signatures are commonly observed in local ion and electron measurements as Cassini traverses the inner magnetosphere. Based on the geometry of the pass, the spacecraft typically observes the more energetic ions from a recent injections before the less energetic ones. Gradient-curvature drifts increase with energy for ions. Electrons can be observed either with the higher energies from an injection first or the lower first. Now we have observed ions in both senses. With Cassini, we have had the opportunity to consider these injected distributions as they evolve globally. Dispersion signatures have been observed globally in energetic neutral atom (ENA) images obtained by the Ion Neutral CAmera (INCA) and show energy-dependent spiral patterns. We seek consistency between the locally and globally observed ion dispersions. We model the drifts of global energetic ion distributions whose general morphology is derived from ENA measurements. The total drift speed consists of the usual ExB drift and the purely magnetic drift due to the curvature and gradient of the magnetic field. The rotational electric field is derived from measurements of the cold plasma rotation speed as a function of radius from the Voyager flybys. The results show that injected ion distribution evolve into spirals with different shapes and phase shift depending on energy. The apparent contradiction of low energy ions arriving before high energy ions can be reproduced by allowing for several revolutions of the ion distribution so that high energy ions simply overtake the low energy ions. By comparing this modeling to the local and global observation it allows tracking of the distributions back to their original injection and helps determine lifetimes of various particles in the inner magnetosphere of Saturn.
C:son Brandt Pontus
Krimigis Stamatios M.
Krupp Norbert
Mauk Barry H.
Mitchell Donald G.
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