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Sustained lobe reconnection in Saturn's magnetotail

Sustained lobe reconnection in Saturn's magnetotail
Sustained lobe reconnection in Saturn's magnetotail

The degree to which solar wind driving may affect Saturn's magnetosphere is not yet fully understood. We present observations that suggest that under some conditions the solar wind does govern the character of the plasma sheet in Saturn's outer magnetosphere. On 16 September 2006, the Cassini spacecraft, at a radial distance of 37 Rs near local midnight, observed a sunward flowing ion population for ∼5 h, which was accompanied by enhanced Saturn Kilometric Radiation emissions. We interpret this beam as the outflow from a long-lasting episode of Dungey-type reconnection, i.e., reconnection of previously open flux containing magnetosheath material. The beam occurred in the middle of a several-day interval of SKR activity and enhanced lobe magnetic field strength, apparently caused by the arrival of a solar wind compression region with significantly higher than average dynamic pressure. The arrival of the high-pressure solar wind also marked a change in the composition of the plasma-sheet plasma, from water-group-dominated material clearly of inner-magnetosphere origin to material dominated by light-ion composition, consistent with captured magnetosheath plasma. This event suggests that under the influence of prolonged high solar wind dynamic pressure, the tail plasma sheet, which normally consists of inner-magnetospheric plasma, is eroded away by ongoing reconnection that then involves open lobe field lines. This process removes open magnetic flux from the lobes and creates a more Earth-like, Dungey-style outer plasma sheet dominantly of solar wind origin. This behavior is potentially a recurrent phenomenon driven by repeating high-pressure streams (corotating interaction regions) in the solar wind, which also drive geomagnetic storms at Earth.

magnetosphere, magnetotail, Saturn
2169-9380
10257-10274
Thomsen, M. F.
bc09abeb-5d20-449f-9f54-568fff6d220c
Jackman, C. M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Mitchell, D. G.
990d4f16-a95d-46ed-9d79-175bd5ea336d
Hospodarsky, G.
a8e798f4-dbcf-49c5-8e82-24c279fd6596
Kurth, W. S.
68ef824f-23ee-4e70-8b4c-b64021b7a3b9
Hansen, K. C.
992a66ab-34d3-4cda-bc0c-816b899a4025
Thomsen, M. F.
bc09abeb-5d20-449f-9f54-568fff6d220c
Jackman, C. M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Mitchell, D. G.
990d4f16-a95d-46ed-9d79-175bd5ea336d
Hospodarsky, G.
a8e798f4-dbcf-49c5-8e82-24c279fd6596
Kurth, W. S.
68ef824f-23ee-4e70-8b4c-b64021b7a3b9
Hansen, K. C.
992a66ab-34d3-4cda-bc0c-816b899a4025

Thomsen, M. F., Jackman, C. M., Mitchell, D. G., Hospodarsky, G., Kurth, W. S. and Hansen, K. C. (2015) Sustained lobe reconnection in Saturn's magnetotail. Journal of Geophysical Research: Space Physics, 120 (12), 10257-10274. (doi:10.1002/2015JA021768).

Record type: Article

Abstract

The degree to which solar wind driving may affect Saturn's magnetosphere is not yet fully understood. We present observations that suggest that under some conditions the solar wind does govern the character of the plasma sheet in Saturn's outer magnetosphere. On 16 September 2006, the Cassini spacecraft, at a radial distance of 37 Rs near local midnight, observed a sunward flowing ion population for ∼5 h, which was accompanied by enhanced Saturn Kilometric Radiation emissions. We interpret this beam as the outflow from a long-lasting episode of Dungey-type reconnection, i.e., reconnection of previously open flux containing magnetosheath material. The beam occurred in the middle of a several-day interval of SKR activity and enhanced lobe magnetic field strength, apparently caused by the arrival of a solar wind compression region with significantly higher than average dynamic pressure. The arrival of the high-pressure solar wind also marked a change in the composition of the plasma-sheet plasma, from water-group-dominated material clearly of inner-magnetosphere origin to material dominated by light-ion composition, consistent with captured magnetosheath plasma. This event suggests that under the influence of prolonged high solar wind dynamic pressure, the tail plasma sheet, which normally consists of inner-magnetospheric plasma, is eroded away by ongoing reconnection that then involves open lobe field lines. This process removes open magnetic flux from the lobes and creates a more Earth-like, Dungey-style outer plasma sheet dominantly of solar wind origin. This behavior is potentially a recurrent phenomenon driven by repeating high-pressure streams (corotating interaction regions) in the solar wind, which also drive geomagnetic storms at Earth.

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Published date: 6 November 2015
Keywords: magnetosphere, magnetotail, Saturn

Identifiers

Local EPrints ID: 436468
URI: http://eprints.soton.ac.uk/id/eprint/436468
ISSN: 2169-9380
PURE UUID: 9de6ecf5-0499-460d-8047-1c1a7f4007b5
ORCID for C. M. Jackman: ORCID iD orcid.org/0000-0003-0635-7361

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Date deposited: 11 Dec 2019 17:30
Last modified: 07 Oct 2020 02:04

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Contributors

Author: M. F. Thomsen
Author: C. M. Jackman ORCID iD
Author: D. G. Mitchell
Author: G. Hospodarsky
Author: W. S. Kurth
Author: K. C. Hansen

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