Cassini observations of Saturn's magnetospheric cusp

• Main Author: Jasinski, J. M.
• Published: University College London (University of London) 2015
• Subjects: 523.46
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.674673

The magnetospheric cusp is a funnel-shaped region where shocked solar wind plasma is able to enter the high latitude magnetosphere via the process of magnetic reconnection. The first in-situ analysis of the cusp region at Saturn is presented using data from the Cassini spacecraft, primarily from particle instruments and magnetic field observations. The analysis is presented in three sections. Firstly, two high-latitude spacecraft crossings are confirmed to be cusp observations by: (i) comparing the observed plasma with that of the magnetosheath and the adjacent magnetosphere, (ii) investigating the direction of the observed ions and (iii) analysing the composition of the plasma. The ion observations are shown to be a result of `bursty' reconnection occurring at the dayside magnetopause. The field-aligned distances to the reconnection site are calculated from the observed energy-pitch angle dispersions. Secondly, all the observations of the cusp are presented for the high latitude spacecraft orbits between 2007 and 2013. A comparison of the observations is made as well as classification into groups due to varying characteristics. The locations of the reconnection site are calculated and compared to the literature. The events are also compared to solar wind propagation models to investigate any correlations. Finally, the magnetic field observations of the cusps are analysed, focusing on the diamagnetic depressions. This characteristic is not observed in all of the cusps, and the possible explanations for this are discussed. The data are subtracted from a magnetic field model, and the calculated magnetic pressure deficits are compared to the particle pressures. A high plasma pressure layer in the magnetosphere adjacent to the cusp is discovered to also depress the magnetic field. A summary of the consequences of this work is discussed specifically regarding the ongoing debate of the role of reconnection at Saturn and its influence on magnetospheric dynamics.