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Planetary period modulation of reconnection bursts in Saturn's magnetotail

Planetary period modulation of reconnection bursts in Saturn's magnetotail
Planetary period modulation of reconnection bursts in Saturn's magnetotail

We conduct a statistical analysis of 2,094 reconnection events in Saturn's near-equatorial magnetotail previously identified in Cassini magnetometer data from intervals during 2006 and 2009/2010. These consist of tailward propagating plasmoids and planetward propagating dipolarizations, with approximately twice as many plasmoids as dipolarizations. We organize these by three related planetary period oscillation (PPO) phase systems, the northern and southern PPO phases relative to noon, the same phases retarded by a radial propagation delay, and the local retarded phases that take account of the azimuth (local time) of the observation. Clear PPO modulation is found for both plasmoid and dipolarization events, with local retarded phases best organizing the event data with the modulation in event frequency propagating across the tail as the PPO systems rotate. This indicates that the events are localized in azimuth, rather than simultaneously affecting much of the tail width. Overall, events occur preferentially by factors of ~3 at northern and southern phases where the tail current sheet is expected locally to be thinnest in the PPO cycle, with field lines contracting back from their maximum radial displacement, compared with the antiphase conditions. Separating the events into those representing the start of independent reconnection episodes, occurring at least 3 hr after the last, and events in subsequent clusters, shows that the above phases are predominantly characteristic of the majority cluster events. The phases at the start of independent reconnection episodes are typically ~60° earlier.

dipolarization, magnetic reconnection, magnetotail, plasmoid, PPO, Saturn
2169-9380
9476-9507
Bradley, T. J.
d4cce4f3-bb69-4e14-baee-cd6a88e38101
Cowley, S. W.H.
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Bunce, E. J.
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Smith, A. W.
f719dbf6-612c-4ecb-9ec8-ae0ac74928eb
Jackman, C. M.
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Provan, G.
5de9f25e-ab6f-4c99-aeec-e45394a48a6b
Bradley, T. J.
d4cce4f3-bb69-4e14-baee-cd6a88e38101
Cowley, S. W.H.
03532d56-a8de-4555-8c69-0fb82fbe9ee0
Bunce, E. J.
fcf0aef9-5e8c-4fc0-b8b8-5a0bfbbd0079
Smith, A. W.
f719dbf6-612c-4ecb-9ec8-ae0ac74928eb
Jackman, C. M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Provan, G.
5de9f25e-ab6f-4c99-aeec-e45394a48a6b

Bradley, T. J., Cowley, S. W.H., Bunce, E. J., Smith, A. W., Jackman, C. M. and Provan, G. (2018) Planetary period modulation of reconnection bursts in Saturn's magnetotail. Journal of Geophysical Research: Space Physics, 123 (11), 9476-9507. (doi:10.1029/2018JA025932).

Record type: Article

Abstract

We conduct a statistical analysis of 2,094 reconnection events in Saturn's near-equatorial magnetotail previously identified in Cassini magnetometer data from intervals during 2006 and 2009/2010. These consist of tailward propagating plasmoids and planetward propagating dipolarizations, with approximately twice as many plasmoids as dipolarizations. We organize these by three related planetary period oscillation (PPO) phase systems, the northern and southern PPO phases relative to noon, the same phases retarded by a radial propagation delay, and the local retarded phases that take account of the azimuth (local time) of the observation. Clear PPO modulation is found for both plasmoid and dipolarization events, with local retarded phases best organizing the event data with the modulation in event frequency propagating across the tail as the PPO systems rotate. This indicates that the events are localized in azimuth, rather than simultaneously affecting much of the tail width. Overall, events occur preferentially by factors of ~3 at northern and southern phases where the tail current sheet is expected locally to be thinnest in the PPO cycle, with field lines contracting back from their maximum radial displacement, compared with the antiphase conditions. Separating the events into those representing the start of independent reconnection episodes, occurring at least 3 hr after the last, and events in subsequent clusters, shows that the above phases are predominantly characteristic of the majority cluster events. The phases at the start of independent reconnection episodes are typically ~60° earlier.

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More information

Accepted/In Press date: 1 November 2018
e-pub ahead of print date: 6 November 2018
Published date: November 2018
Keywords: dipolarization, magnetic reconnection, magnetotail, plasmoid, PPO, Saturn

Identifiers

Local EPrints ID: 426938
URI: https://eprints.soton.ac.uk/id/eprint/426938
ISSN: 2169-9380
PURE UUID: 7110e343-cd79-409c-b14a-372d17f0ea53
ORCID for T. J. Bradley: ORCID iD orcid.org/0000-0001-6568-5811
ORCID for A. W. Smith: ORCID iD orcid.org/0000-0001-7321-4331

Catalogue record

Date deposited: 18 Dec 2018 17:30
Last modified: 03 Dec 2019 01:34

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