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Evidence for periodic variations in the thickness of Saturn’s nightside plasma sheet

Evidence for periodic variations in the thickness of Saturn’s nightside plasma sheet
Evidence for periodic variations in the thickness of Saturn’s nightside plasma sheet
During certain portions of the Cassini mission to Saturn, Cassini made repeated and periodic crossings of the magnetospheric current sheet that lies near the magnetic equator and extends well down the magnetospheric tail. These repeated crossings are part of the puzzling set of planetary period variations in numerous magnetospheric properties that have been discovered at Saturn. During 2010 these periodic crossings often display asymmetries such that the northbound crossing occurs faster than the southbound crossing or vice versa, while at other times the crossings are more symmetric. The character of the crossings is well organized by the relative phase of the northern versus southern perturbation currents inferred in earlier analyses of the magnetic field observations. Further, the dependence of the character of the crossings on the relative phase is consistent with similar asymmetries predicted both by the dual rotating current systems inferred from magnetic field observations and by global MHD models that incorporate the effects of hypothesized atmospheric vortices. The two models are themselves in generally good agreement on those predictions. In both models the asymmetries are attributable to a periodic thickening and thinning of the magnetospheric current sheet, combined with a periodic vertical flapping of the sheet. The Cassini observations thus provide additional observational support to such current systems as a likely explanation for many of the known magnetospheric planetary period variations.
2169-9380
280-292
Thomsen, M.F.
81992bfc-27a7-42f3-9e36-571ce61228a6
Jackman, Caitriona
9bc3456c-b254-48f1-ade0-912c5b8b4529
Cowley, S.W.H.
03532d56-a8de-4555-8c69-0fb82fbe9ee0
Jia, X.
abd6edaf-e6d8-4659-9abf-38fcd6a6f288
Kivelson, M.G
4ae163e2-1ab4-4ae8-88ab-4744c65f9986
Provan, G.
b494905b-ef77-4973-8135-8660ae925473
Thomsen, M.F.
81992bfc-27a7-42f3-9e36-571ce61228a6
Jackman, Caitriona
9bc3456c-b254-48f1-ade0-912c5b8b4529
Cowley, S.W.H.
03532d56-a8de-4555-8c69-0fb82fbe9ee0
Jia, X.
abd6edaf-e6d8-4659-9abf-38fcd6a6f288
Kivelson, M.G
4ae163e2-1ab4-4ae8-88ab-4744c65f9986
Provan, G.
b494905b-ef77-4973-8135-8660ae925473

Thomsen, M.F., Jackman, Caitriona, Cowley, S.W.H., Jia, X., Kivelson, M.G and Provan, G. (2017) Evidence for periodic variations in the thickness of Saturn’s nightside plasma sheet. Journal of Geophysical Research: Space Physics, 122 (1), 280-292. (doi:10.1002/2016JA023368).

Record type: Article

Abstract

During certain portions of the Cassini mission to Saturn, Cassini made repeated and periodic crossings of the magnetospheric current sheet that lies near the magnetic equator and extends well down the magnetospheric tail. These repeated crossings are part of the puzzling set of planetary period variations in numerous magnetospheric properties that have been discovered at Saturn. During 2010 these periodic crossings often display asymmetries such that the northbound crossing occurs faster than the southbound crossing or vice versa, while at other times the crossings are more symmetric. The character of the crossings is well organized by the relative phase of the northern versus southern perturbation currents inferred in earlier analyses of the magnetic field observations. Further, the dependence of the character of the crossings on the relative phase is consistent with similar asymmetries predicted both by the dual rotating current systems inferred from magnetic field observations and by global MHD models that incorporate the effects of hypothesized atmospheric vortices. The two models are themselves in generally good agreement on those predictions. In both models the asymmetries are attributable to a periodic thickening and thinning of the magnetospheric current sheet, combined with a periodic vertical flapping of the sheet. The Cassini observations thus provide additional observational support to such current systems as a likely explanation for many of the known magnetospheric planetary period variations.

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Evidence for periodic variations in the thicknessof Saturn’s nightside plasma sheet - Accepted Manuscript
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Accepted/In Press date: 16 November 2016
e-pub ahead of print date: 6 December 2016
Published date: January 2017

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Local EPrints ID: 412921
URI: https://eprints.soton.ac.uk/id/eprint/412921
ISSN: 2169-9380
PURE UUID: 5181cfd8-5e54-4e7f-810d-f3e92f2a2bca

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Date deposited: 08 Aug 2017 16:31
Last modified: 02 Dec 2019 18:57

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Contributors

Author: M.F. Thomsen
Author: S.W.H. Cowley
Author: X. Jia
Author: M.G Kivelson
Author: G. Provan

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