Rymer, Abigail Mary; (2004) Analysis of Cassini plasma and magnetic field measurements from 1-7 AU. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Cassini was launched in October 1997. Since then it has performed four planetary swing-bys and collected hundreds of days of data in the solar wind. In this thesis we mainly use data from the Cassini Electron Spectrometer (ELS) to discuss low energy electron distributions observed from 1 to 7 AU, and during the Cassini swing-bys of Earth and Jupiter. A method to estimate the spacecraft potential and calculate electron density and temperature by examining one dimensional cuts through the electron distributions is first introduced. These data are used to introduce many equatorial regions of the Earth's magnetosphere as observed by ELS in August 1999. We discuss ELS measurements of the upstream solar wind, the Earth's bow shock, magnetopause, day and nightside magnetosphere, radiation belts, low latitude boundary layer, and the plasmasheet. It is believed the encounter happened whilst reconnection was occurring at the nose of the magnetosphere, and hence we encountered an eroding magnetosphere with signatures of two substorms during the outbound path. The Cassini crossing of the Earth's bow shock is compared to statistical results gained during ~40 crossings by Cassini of Jupiter's bow shock. We find that observations of the electron temperature jump are consistent with that observed at the Earth, suggesting that the same fundamental processes are involved at both systems. Cassini-ELS observations of solar wind electron temperature are then discussed in the context of previous work. Based on ELS data alone we find that the solar wind electron temperature decreases with increasing heliocentric distance and that this decrease is slightly faster than predicted by Parker/two fluid models, slower than expected for adiabatic expansion and toward the steeper end of the scale based on previous observations.

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