Magnetospheric plasma dynamics : investigating ion and electron flow in the magnetotail

Doyle, Jonathan and Wild, Jim (2019) Magnetospheric plasma dynamics : investigating ion and electron flow in the magnetotail. PhD thesis, Lancaster University.

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Abstract

An investigation was carried out using moment data from the Cluster CIS and PEACE instruments, examining earthward and tailward directed ion and electron flows within the terrestrial magnetotail. For a time interval spanning 2001-2006, the study looked at the distribution of ion bulk velocity vectors in the magnetotail, separating the region up into discreet slices in the XY plane, and later in the XZ plane. Key features of the ion velocity distribution and flow directions were uncovered, highlighting how ions behave within the magnetotail over large time periods and helping to form a greater understanding of the overall picture of the Earth’s magnetosphere. The results found are in general agreement with a number of similar studies previously carried out on topic, and found that overall, the magnetosphere is a rather stagnant system. An important mechanism in the terrestrial magnetosphere is the transportation of energy and momentum throughout the system. Magnetospheric substorms have been linked to much of this transportation and as such, the investigation in this thesis shifts the focus from the occurrence of plasma flow for all times, to just during substorm events, concentrating on the three substorm phases, the growth expansion and recovery phase. The duration of each phase is quite short, meaning that the amount of data available was somewhat limited. This led to the time interval used to be increased to 14 years. Observations of key differences in the velocity distributions and flow patterns between each substorm phase were made, and the dominant direction of ion flow was found, both at the equatorial plane and further out into the magnetospheric lobes. The final investigation looked at how the data availability could be increased in order to improve the quality and reliability of the results. Following the frozen-in theorem, all charged particles are constrained to their local magnetic field lines and as such, they should all follow the same general flow pattern. An attempt was made to recreate the results of the first study instead using PEACE electron moments. If it was found to be possible, both data sets could be combined to greatly increase the resolution of the results. The electron velocity distribution was investigated and the dominant electron flow direction was found to be tailward within the plasma sheet, the opposite of ion flows. A further examination of the results was carried out to establish what could be causing tailward flow dominance in this region and in conclusion, it was decided that until a more in-depth investigation is carried out, PEACE electron moments are unsuitable for large time scale analysis of magnetospheric plasma flows.