Evidence for rotationally driven plasma transport in Saturn's magnetosphere - art. no. L14S10

摘要

[ 1] Radial convective transport of plasma in a rotation-dominated 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 (similar to 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 RS ( Saturn's radius) but range up to several RS. 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.