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Configuration and Dynamics of Saturn's Disc-Like Magnetosphere

Sorba, Arianna M.; (2019) Configuration and Dynamics of Saturn's Disc-Like Magnetosphere. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This thesis explores how the con guration and dynamics of Saturn's magnetosphere are controlled by internal and external in uences. Saturn's magnetosphere has signi cant internal plasma sources; cold, dense plasma in the equatorial region originating from its moon Enceladus, and a hotter, more variable population in the outer magnetosphere. The hot plasma in uences the magnetic eld structure via enhancement of the ring current, and also a ects pressure balance at the magnetopause. This pressure balance controls how compressible the magnetosphere is in response to changing solar wind conditions. Using a 2-D force-balance model of Saturn's magnetodisc, we nd that Saturn's magnetosphere is more compressible when the global hot plasma content is greater, and as the magnetosphere expands. We suggest this behaviour is predominantly driven by a recon guration of the magnetic eld into a more disc-like structure under such conditions. In addition, periodic variations have been observed throughout Saturn's mag- netosphere, at a period close to the planetary rotation rate. Recent studies suggest the equatorial current sheet periodically ` aps' above and below the rotational equa- tor, and `breathes' in and out with varying current sheet thickness, in response to dual rotating magnetic perturbations. To investigate this behaviour, we use a family of force-balance models of di erent sizes in combination with a geometric current sheet model, and compare the results to magnetic eld data measured by the Cassini spacecraft in late 2009. We nd that including the breathing behaviour in the model signi cantly improves model-data agreement, particularly for the meridional com- ponent of the magnetic eld. Finally, the con guration of Saturn's magnetosphere across local time is investi- gated. Average pro les of hot plasma pressure calculated from Cassini observations are used as inputs to force-balance models of di erent sizes, to represent di er- ent local time sectors. The results demonstrate that local time variations in the hot plasma population and e ective magnetodisc radius can signi cantly in uence global magnetospheric structure.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Configuration and Dynamics of Saturn's Disc-Like Magnetosphere
Event: University College London (UCL)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms.
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10077563
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