Magnetic field studies of Jupiter in the Juno era

This thesis reports on studies of magnetic field observations obtained by the NASA Juno spacecraft currently orbiting Jupiter. The first study covers the analysis of the first 10 inbound data-taking Juno orbits, where we determine the high-altitude perturbation azimuthal magnetic field associated with a field-aligned magnetosphereionosphere coupling current system associated with a breakdown in corotation between the planet and magnetospheric plasma. We compare our results with a steadystate axisymmetric magnetosphere-ionosphere coupling model developed by Cowley et al. (2005, 2008, 2017), and find that although the overall shape of the data and model are consistent, the field-aligned current signatures are a factor ∼1.5 weaker than the model prediction. We also determine that the location of the field-aligned current sheets and the main oval emission are closely linked. The second study involves a comparison between concurrent and near-concurrent Juno magnetic field and ultraviolet spectrometer observations, to determine if there is any relationship between the fieldaligned current signatures and the mapped ultraviolet brightness, and we compare the signatures with predictions of the previously mentioned model. We find that the magnitude of the perturbation azimuthal magnetic field and corresponding ionospheric Pedersen current for the concurrent observations are linked to the mapped ultraviolet auroral brightness of the main emission. The third study investigates the first 15 datataking Juno orbits, where we analyse the magnetic field associated with the equatorial current sheet in the middle magnetosphere. We analyse the perturbation radial magnetic field associated with the current sheet and develop simple models of this field with respect to radial distance and local time. We also analyse the axial magnetic field dominant in the current sheet centre and develop a simple model of this field with respect to radial distance.