HR: 09:00h
AN: SM11A-03    [Abstracts]
TI: Magnetospheric Drift Resonance Effects on Local Time Asymmetry, Injection Events, and Moon Interactions for Saturn as Compared to Earth
AU: * Cooper, J F
EM: John.F.Cooper@nasa.gov
AF: NASA Goddard Space Flight Center, Code 612.4, Space Physics Data Facility, 8800 Greenbelt Road, Greenbelt, MD 20771 United States
AB: The magnetospheres of Earth and Saturn have similarities in terms of the highest energy radiation belt components from Cosmic Ray Albedo Neutron Decay (CRAND) but have otherwise been expected to differ on the role of charged particle convection driven by solar wind interactions with these magnetospheres. Saturn's inner and middle magnetosphere has been assumed to be dominated by corotation with little direct penetration by solar wind and magnetotail plasma. Since Saturn's planetary magnetic field characterized by the Z3 model is axisymmetric, although slightly offset northward from the ring plane, it has been difficult to understand previous Pioneer and Voyager measurements of local time asymmetry in energetic particle populations, including just outside the main rings as found by Pioneer 11. Small scale features (microsignatures) of charged particle absorption by Saturn moons and possible 'ghost' clouds of co-orbiting debris show no consistent patterns in the context of symmetric models for longitudinal drift shells. Since the 100-MeV CRAND proton drift shells are highly symmetric, it is apparent that lower energy electrons and ions showing substantial local time asymmetry are influenced by forces other than simple corotation. Cassini Huygens neutral atom observations show clear evidence of substorm injections reaching into the middle magnetosphere of Saturn preferentially on the nightside. One model would be that hot magnetotail plasma is convecting sunward into regions of colder plasma previously observed by Voyager, consistent with a dusk-to-dawn convective electric field. Numerical simulations of keV to MeV electron motion under such conditions, and with variability of upstream solar wind speed and magnetic field, show large perturbations of electron drift shells maximizing at energies of drift resonance where retrograde gradient-cuvature drift exactly cancels corotation for electrons at energies above several hundred keV. Averaged over many drift periods these perturbations produce the previously observed local time asymmetries in electron flux while also providing alternatives to formation of the detected moon microsignatures. Analysis of electron and ion flux distributions in Saturn magnetospheric longitude may provide sensitive measures of large scale electric fields.
DE: 2732 Magnetosphere interactions with satellites and rings
DE: 2740 Magnetospheric configuration and dynamics
DE: 2756 Planetary magnetospheres (5443, 5737, 6030)
DE: 2784 Solar wind/magnetosphere interactions
DE: 5737 Magnetospheres (2756)
SC: SPA-Magnetospheric Physics [SM]
MN: 2005 Joint Assembly