Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm23a1931k&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM23A-1931
Physics
[2740] Magnetospheric Physics / Magnetospheric Configuration And Dynamics, [2756] Magnetospheric Physics / Planetary Magnetospheres
Scientific paper
On numerous orbits that explored the dusk side magnetotail during 2009-2010, the Ion and Neutral Camera (INCA) instrument on the Cassini spacecraft has detected fluxes of hot ions. We have analyzed ion data during this period and found that plasma in the dusk-midnight quadrant sub-corotates, albeit at a large fraction of the rigid corotation speed, with the primary velocity being azimuthal but with a distinct outward component. The velocities, measured beyond ~20 Rs, are similar to those obtained from earlier orbits in the midnight-dawn sector, in contrast to the depressed velocities measured at Jupiter in the dusk-midnight quadrant, using Energetic Particles Detector (EPD) measurements on the Galileo spacecraft. These INCA data at Saturn along with previous results are consistent with a plasma disk undergoing a centrifugally induced expansion as it emerges into the night side, while maintaining partial rotation with the planet. From earlier and present Saturn studies, the magnetodisk expansion continues as plasma rotates across the tail to the dawn side. In neither magnetotail do we see evidence for steady state reconnection, despite the significant asymmetry in the convection velocity at Jupiter. We have noted previously that in the outer regions of the night side magnetodisk, equatorial plasma azimuthal speeds plateau (as a function of radial distance) at both Jupiter and Saturn, at distances in the night side beyond the magnetopause standoff distance. The outermost region of the magnetodisk, having undergone expansion upon emerging from the day side magnetopause confinement, is unlikely to recirculate back into the dayside. We present a scenario in which plasma confined in a magnetodisk (at either planet) emerges from the day side, expands at the dusk flank, but continues moving around the planet, across the tail, and loses mass at its outer edges primarily near the dawn flank of the magnetotail. The Kelvin-Helmholtz instability provides vorticies to enhance plasma reconnection and diffusion to transport mass down the tail and out of the system.
Carbary James F.
Kane Mark
Krimigis Stamatios M.
Mitchell Donald G.
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