Cassini/CAPS observations of duskside tail dynamics at Saturn

Thomsen, M. F., Wilson, R. J., Tokar, R. L., Reisenfeld, D. B. and Jackman, C. M. (2013) Cassini/CAPS observations of duskside tail dynamics at Saturn. Journal of Geophysical Research: Space Physics, 118 (9), 5767-5781. (doi:10.1002/jgra.50552).

Abstract

Plasma properties of Saturn's premidnight tail region are surveyed using Cassini/Cassini Plasma Spectrometer (CAPS) ion observations from 2010. Only low-latitude (|lat| < 6°) intervals in which the CAPS viewing was roughly symmetric inward and outward around the corotation direction are used. Our numerical moments algorithm returns nonzero ion density for 70% (999) of the intervals selected. Of these, 642 had detectable water-group ion densities, and the remainder were dominantly, if not entirely, light ions. The derived plasma parameters are similar to those found in an earlier study for the postmidnight tail region, except that we find little evidence for the systematic outflows identified in that study, and we do find numerous significant inflow events. One such inflow is identified as a dipolarization event, the first reported plasma properties of such a structure at Saturn. A second, long-lasting event may be evidence for the existence at times of a quasi-steady reconnection region in the premidnight tail. The large majority of the plasma flows are found to be within 20° of the corotation direction, though with flow speeds significantly lower than full corotation. While the inflow events represent plausible evidence for internally driven mass loss in the premidnight region, the absence of significant outflow events suggests that in the region surveyed here, tail reconnection has not yet proceeded to involve lobe field lines, so the disconnected plasma continues its general motion in the corotation direction. Key Points Presents plasma properties in the pre-midnight region of Saturn's magnetotail. Subcorotation dominates the observed flows, with some inflows and outflows. Possible signatures of dipolarization and quasi-steady reconnection are shown.

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Contributors

Author: C. M. Jackman

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