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Cassini/CAPS observations of duskside tail dynamics at Saturn

Cassini/CAPS observations of duskside tail dynamics at Saturn
Cassini/CAPS observations of duskside tail dynamics at Saturn

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 magnetotailSubcorotation dominates the observed flows, with some inflows and outflowsPossible signatures of dipolarization and quasi-steady reconnection are shown.

magnetosphere, Saturn
2169-9380
5767-5781
Thomsen, M. F.
710c64ce-779f-4088-8e50-f9e450232f5f
Wilson, R. J.
29353e8b-14e8-46b9-b5f0-91838ba7fc30
Tokar, R. L.
8213ad4b-5b3b-46b1-90ad-334b61c2d79c
Reisenfeld, D. B.
146943bf-0a2f-47a8-b1d3-208e2d0487b2
Jackman, C. M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Thomsen, M. F.
710c64ce-779f-4088-8e50-f9e450232f5f
Wilson, R. J.
29353e8b-14e8-46b9-b5f0-91838ba7fc30
Tokar, R. L.
8213ad4b-5b3b-46b1-90ad-334b61c2d79c
Reisenfeld, D. B.
146943bf-0a2f-47a8-b1d3-208e2d0487b2
Jackman, C. M.
9bc3456c-b254-48f1-ade0-912c5b8b4529

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).

Record type: Article

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 magnetotailSubcorotation dominates the observed flows, with some inflows and outflowsPossible signatures of dipolarization and quasi-steady reconnection are shown.

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More information

Accepted/In Press date: 6 September 2013
e-pub ahead of print date: 12 September 2013
Published date: September 2013
Keywords: magnetosphere, Saturn

Identifiers

Local EPrints ID: 436535
URI: http://eprints.soton.ac.uk/id/eprint/436535
ISSN: 2169-9380
PURE UUID: da69e5e6-6951-4b4f-abf6-afbc6e039197
ORCID for C. M. Jackman: ORCID iD orcid.org/0000-0003-0635-7361

Catalogue record

Date deposited: 12 Dec 2019 17:30
Last modified: 10 Nov 2021 03:35

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Contributors

Author: M. F. Thomsen
Author: R. J. Wilson
Author: R. L. Tokar
Author: D. B. Reisenfeld
Author: C. M. Jackman ORCID iD

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