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Reconnection in a rotation-dominated magnetosphere and its relation to Saturn's auroral dynamics

Reconnection in a rotation-dominated magnetosphere and its relation to Saturn's auroral dynamics
Reconnection in a rotation-dominated magnetosphere and its relation to Saturn's auroral dynamics

The first extended series of observations of Saturn's auroral emissions, undertaken by the Hubble Space Telescope in January 2004 in conjunction with measurements of the upstream solar wind and interplanetary magnetic field (IMF) by the Cassini spacecraft, have revealed a strong auroral response to the interplanetary medium. Following the arrival of the forward shock of a corotating interaction region compression, bright auroras were first observed to expand significantly poleward in the dawn sector such that the area of the polar cap was much reduced, following which the auroral morphology evolved into a spiral structure around the pole. We propose that these auroral effects are produced by compression-induced reconnection of a significant fraction of the open flux present in Saturn's open tail lobes, as has also been observed to occur at Earth, followed by subcorotation of the newly closed flux tubes in the outer magnetosphere region due to the action of the ionospheric torque. We show that the combined action of reconnection and rotation naturally gives rise to spiral structures on newly opened and newly closed field lines, the latter being in the same sense as observed in the auroral images. The magnetospheric corollary of the dynamic scenario outlined here is that corotating interaction region-induced magnetospheric compressions and tail collapses should be accompanied by hot plasma injection into the outer magnetosphere, first in the midnight and dawn sector, and second at increasing local times via noon and dusk. We discuss how this scenario leads to a strong correlation of auroral and related disturbances at Saturn with the dynamic pressure of the solar wind, rather than to a correlation with the north-south component of the IMF as observed at Earth, even though the underlying physics is similar, related to the transport of magnetic flux to and from the tail in the Dungey cycle.

2169-9380
1-19
Cowley, S.W.H.
e8174910-ddcd-4a23-9d7c-0e1117def06c
Badman, S.V.
d5bc36ea-0df0-49e9-b367-8db1f9a95e11
Bunce, E.J.
208e1177-a92f-47a6-878d-ef27ed03f811
Clarke, J.T.
51f1aa84-81b2-43fa-8300-3fb591f5dac5
Gérard, J.C.
d0fbbdb4-16cd-4f55-869e-e16992111809
Grodent, D.
9f63c3db-559c-49b9-b9ad-28b0168a8443
Jackman, C.M.
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Milan, S.E.
b6dd5367-b0c4-4f30-953a-f2d13078d656
Yeoman, T.K.
cc3f7732-a6a5-462e-aa81-289804631314
Cowley, S.W.H.
e8174910-ddcd-4a23-9d7c-0e1117def06c
Badman, S.V.
d5bc36ea-0df0-49e9-b367-8db1f9a95e11
Bunce, E.J.
208e1177-a92f-47a6-878d-ef27ed03f811
Clarke, J.T.
51f1aa84-81b2-43fa-8300-3fb591f5dac5
Gérard, J.C.
d0fbbdb4-16cd-4f55-869e-e16992111809
Grodent, D.
9f63c3db-559c-49b9-b9ad-28b0168a8443
Jackman, C.M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Milan, S.E.
b6dd5367-b0c4-4f30-953a-f2d13078d656
Yeoman, T.K.
cc3f7732-a6a5-462e-aa81-289804631314

Cowley, S.W.H., Badman, S.V., Bunce, E.J., Clarke, J.T., Gérard, J.C., Grodent, D., Jackman, C.M., Milan, S.E. and Yeoman, T.K. (2005) Reconnection in a rotation-dominated magnetosphere and its relation to Saturn's auroral dynamics. Journal of Geophysical Research: Space Physics, 110 (A2), 1-19, [A02201]. (doi:10.1029/2004JA010796).

Record type: Article

Abstract

The first extended series of observations of Saturn's auroral emissions, undertaken by the Hubble Space Telescope in January 2004 in conjunction with measurements of the upstream solar wind and interplanetary magnetic field (IMF) by the Cassini spacecraft, have revealed a strong auroral response to the interplanetary medium. Following the arrival of the forward shock of a corotating interaction region compression, bright auroras were first observed to expand significantly poleward in the dawn sector such that the area of the polar cap was much reduced, following which the auroral morphology evolved into a spiral structure around the pole. We propose that these auroral effects are produced by compression-induced reconnection of a significant fraction of the open flux present in Saturn's open tail lobes, as has also been observed to occur at Earth, followed by subcorotation of the newly closed flux tubes in the outer magnetosphere region due to the action of the ionospheric torque. We show that the combined action of reconnection and rotation naturally gives rise to spiral structures on newly opened and newly closed field lines, the latter being in the same sense as observed in the auroral images. The magnetospheric corollary of the dynamic scenario outlined here is that corotating interaction region-induced magnetospheric compressions and tail collapses should be accompanied by hot plasma injection into the outer magnetosphere, first in the midnight and dawn sector, and second at increasing local times via noon and dusk. We discuss how this scenario leads to a strong correlation of auroral and related disturbances at Saturn with the dynamic pressure of the solar wind, rather than to a correlation with the north-south component of the IMF as observed at Earth, even though the underlying physics is similar, related to the transport of magnetic flux to and from the tail in the Dungey cycle.

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Published date: February 2005

Identifiers

Local EPrints ID: 437120
URI: http://eprints.soton.ac.uk/id/eprint/437120
ISSN: 2169-9380
PURE UUID: f427c366-610f-40a0-9525-294473921b2f
ORCID for C.M. Jackman: ORCID iD orcid.org/0000-0003-0635-7361

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Date deposited: 17 Jan 2020 17:34
Last modified: 10 Nov 2021 03:35

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Contributors

Author: S.W.H. Cowley
Author: S.V. Badman
Author: E.J. Bunce
Author: J.T. Clarke
Author: J.C. Gérard
Author: D. Grodent
Author: C.M. Jackman ORCID iD
Author: S.E. Milan
Author: T.K. Yeoman

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