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  • 2019martinphd

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On the modelling and consequence of small-scale magnetic phenomena in the Saturnian system

Research output: ThesisDoctoral Thesis

Published
Publication date2019
Number of pages246
QualificationPhD
Awarding Institution
Supervisors/Advisors
Publisher
  • Lancaster University
Original languageEnglish

Abstract

This thesis presents an analysis of Cassini magnetometer data in two different regions of the Kronian system. An evaluation of aperiodic waves on the equatorial current sheet is presented; the waves are fitted to a model of a Harris current sheet deformed by a Gaussian wave pulse. This analysis allows examination of the parameters relating to the waves, where amplitude of waves is found to increase with radial distance. In addition, the direction of propagation of the waves is found by resolving the wave numbers in 2-dimensions, where a general outwards propagation is found.
The use of the Harris current sheet also allows the resolution of current sheet parameters, and it is found that the scale height of the current sheet increases with radial distance. Additionally, values of the magnetic field in the lobes are found using the model, which are then used along with the scale heights to estimate the current density in the azimuthal and radial directions. These values can also be used to calculate, using the divergence of current, the field aligned currents entering and leaving the ionosphere where a current entering the ionosphere pre-noon and a current exiting the ionosphere post-midnight are shown. This current density is then converted to an electron flux in the upward current region, and could produce an additional 1-11 kR of auroral emission which is seen in other infrared and ultraviolet data sets.
Additionally, irregular magnetic signatures, such as the aperiodic waves, are found in the entire system including Titan’s ionosphere. At Titan, a statistical study of the position of flux ropes finds no spatial dependence other than an increased number of flux ropes in the sun-lit regions and ram-side regions. A comparison of force-free and nonforce free models is utilised to extract the radii and axial magnetic field of the flux ropes, and compare the assumptions required for both models. Additionally, deformations to the models are used to model common asymmetries seen in the magnetometer data and find that bending a force-free flux rope solves the problem of the direction ambiguity of using minimum variance analysis and using elliptical cross-sections of flux ropes allows for a asymmetric flux rope signature.
All together, this thesis explores the varied magnetic phenomena in the Kronian system and uses them to understand the surrounding environment.