Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm22b..08f&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM22B-08
Physics
2431 Ionosphere/Magnetosphere Interactions (2736), 2721 Field-Aligned Currents And Current Systems (2409), 2760 Plasma Convection (2463), 5734 Magnetic Fields And Magnetism, 6275 Saturn
Scientific paper
Saturn's magnetic field is remarkably axisymmetric: its dipole axis is inclined by less than 0.2° with respect to its rotation axis. Recent Cassini observations have revealed small non-axisymmetric field components which rotate slightly more slowly than any atmospheric feature. We show that rotationally driven convection of magnetospheric plasma is responsible for the axisymmetry-breaking. Field-aligned currents transfer angular momentum from the planet to a tongue of outflowing plasma. This transfer slows the rate of rotation of the ionosphere relative to that of the underlying atmosphere. The currents are the source for the non- axisymmetric components of the field. The common rotation rates of these components and Saturn's kilometric radio (SKR) bursts is that of the plasma near the orbit of Enceladus, and by extension the rotation rate in the ionosphere to which this plasma is coupled. That rate tells us nothing about the rotation rate of Saturn's deep interior. Of that we remain ignorant. Magnetic perturbations with magnitudes similar to those observed by Cassini are produced for \dot M ~ 104 g/s, a value similar to estimates for the rate of production of plasma from Saturn's E-ring. Enhancement of the SKR occurs in a narrow range of longitudes where the tip of the outgoing plasma stream connects to the auroral ionosphere, via field lines that are bowed outwards by currents that supply the plasma's centripetal acceleration.
Farmer Alison J.
Goldreich Peter
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