Using modelling and data analysis to interpret single-spacecraft observations in the Jovian and Kronian magnetospheres

Abstract

This thesis deals with the interpretation and expansion upon single-spacecraft observations in the Jovian and Kronian magnetospheres. Unlike at Earth where a host of single and constellation in-situ satellites as well as ground based observations give a good global coverage of the magnetosphere, the magnetospheres of Jupiter and Saturn only have a single spacecraft each, Juno (previously Galileo) at Jupiter and previously Cassini at Saturn. With this local data it is then necessary to expand to a global picture. A "viewing region" is a region within the magnetosphere where we would expect to see the signatures of dynamics that occur within the magnetosphere. Unfortunately, the spacecraft are often not in this ideal region and even if they are, they can still 'miss' dynamics that occur. The work in this thesis looks at how modelling and data analysis can overcome the limits of single-spacecraft observations. The first study looks at a simple avalanching 1-D cellular automata sandpile model as an analogue for magnetospheric dynamics of Jupiter. With simple input and threshold rules, the model can reproduce some statistical properties of the Jovian magnetosphere. The work suggests that much of the mass that is lost from the Jovian magnetosphere is lost in small-scale events that may not be seen by in situ spacecraft or selected by automated detection criteria. The second study looks at the use of low frequency extensions, extensions of the Saturn Kilometric Radiation from higher to lower frequencies, as a proxy for magnetospheric dynamics. An automated criteria is developed for the selection of these events during 2006. Two forms of LFE are found: short events (< 20 hours) which are strongly linked with tail-reconnection events, and long events (> 20 hours) which are strongly linked with increased solar wind dynamic pressure. The third study develops a criteria for the selection of narrowband emissions, a low frequency emission which forms part of the Saturn radio spectrum, and analyses these events in relation to the LFE catalogue developed in the second study, and examines some of their statistical properties. The events are found (as in previous studies) to occur in clusters of usually 5 or 6 individual intensifications over a period of several days following periods of increased solar wind dynamic pressure. In this way narrowband emissions are a good proxy for large-scale events in the magnetosphere.

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Identifiers

ORCID for Caitriona Jackman: orcid.org/0000-0003-0635-7361

ORCID for Daniel Whiter: orcid.org/0000-0001-7130-232X

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