Evidence for rotationally-driven plasma transport in Saturn's magnetosphere
Résumé
Radial convective transport of plasma in a rotationdominated magnetosphere implies alternating longitudinal sectors of cooler, denser plasma moving outward and hotter, more tenuous plasma moving inward. The Cassini Plasma Spectrometer (CAPS) has provided dramatic new evidence of this process operating in the magnetosphere of Saturn. The inward transport of hot plasma is accompanied by adiabatic gradient and curvature drift, producing a V-shaped dispersion signature on a linear energy-time plot. Of the many ($100) such signatures evident during the first two Cassini orbits, we analyze a subset (48) that are sufficiently isolated to allow determination of their ages, widths, and injection locations. Ages are typically <10.8 hr (Saturn's rotation period) but range up to several rotation periods. Widths are typically <1 R S (Saturn's radius) but range up to several R S. Injection locations are randomly distributed in local time and in Saturnian longitude. The apex of the V sometimes coincides with a localized density cavity in the cooler background plasma, and usually coincides with a localized diamagnetic depression of the magnetic field strength. These signatures are fully consistent with the convective motions that are expected to result from the centrifugal interchange instability.
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