Deciphering the Solar Wind Interaction with the Terrestrial and Saturnian Magnetospheres
Creators: name: Gould, Wayne
Publisher: name: Lancaster University
Year: 2024

description: Due to a lack of upstream monitors, the effects of the solar wind on
 Saturn’s magnetosphere are not well understood. Consequently, previous
 investigations of this relationship have been restricted to time limited
 case studies. However, it is known that the solar wind plays an important
 role in magnetosphere dynamics. With the conclusion of the Cassini mission
 in 2017, continuous data, spanning 13 years is available to conduct an
 investigation.
 
 
 In this thesis, we present three studies. The first exploring the
 relationship of directly measured solar wind and IMF data to the magnetic
 field perturbations detected via the geomagnetic indices, AL and SYM/H.
 The second then continues this work with a comparative study between
 coupling functions and their utility versus individual solar wind and IMF
 parameters to detection of the geomagnetic indices, AL and SYM/H. This
 research then culminates in a large-scale statistical study of Saturn
 kilometric radiation as a proxy for the solar wind. Due to the lack of
 direct solar wind monitoring at Saturn, we use a solar wind propagation
 model to explore several solar wind and IMF parameters and their
 relationship with Saturn kilometric radiation.
 
 
 To assess the strength of the relationships between the solar wind
 parameters and both the geomagnetic indices, AL and SYM/H, and Saturn
 kilometric radiation, we use mutual information (chapter 5). Mutual
 information is a measurement of how strong the relationship is between two
 variables, and by extension, how much we can infer from one about the
 other. In the latter study, that is how confident we can be of Saturn
 kilometric radiation’s strength when measuring a given solar wind and IMF
 parameter value from the propagation model. It has significant advantages
 over traditional metrics such as correlation, which can only consider
 linear relationships. Mutual information is able to explore and reveal
 non-linear relationships in addition. This thesis first outlines the
 theory behind and a means of applying mutual information to the data
 considered (chapter 6). Additionally, a means of calculating uncertainties
 for singular data sets is adapted and tested on predictable Gaussian data
 to ascertain the utility of this technique.
 
 
 In our first study (chapter 7) we analyse geomagnetic indices with
 directly measured solar wind data. Known relationships are drawn out in
 expectations with previous studies, confirming the application of the
 methods in this thesis. Our second study (chapter 8) investigates the
 utility of coupling functions as a means of describing the solar wind and
 IMF coupling with the terrestrial magnetosphere, relating them to the
 enhancement of geomagnetic indices. We find that even under general
 conditions, coupling functions are a much stronger indicator of the solar
 wind and IMF relationship to geomagnetic indices.
 
 
 Finally, we apply the methods of this thesis to propagated solar wind and
 IMF data with Saturnian kilometric radiation (chapter 9). We find the IMF
 parameter, By, to present a statistically significant relationship with
 Saturn kilometric radiation, acting as a proxy for the IMF strength and
 rate of magnetic reconnection. Unlike previous case studies that predict
 the dynamic pressure, pdyn, as the strongest relationship, this is found
 to be the weakest relationship of all the parameters considered. However,
 this is related to the uncertainty in propagation arrival times associated
 with the Sun-Earth-Saturn angle and therefore conclude that mutual
 information values for this chapter should be considered a lower limit.
 Further work is then suggested to improve upon these results by relating
 the Sun-Earth-Saturn angle to the time offset described in section 6.4.