Beyene, S; (2013) Understanding the formation of magnetic field and plasma structures in the magnetotail via the reconnection process. Doctoral thesis (PhD), UCL (University College London).

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Abstract

This thesis studies the formation of products of magnetotail reconnection using models and observations. Three studies are presented, the first is an analysis of observations from the Cluster spacecraft, located in different regions of the magnetotail, which allow simultaneous sampling of a Travelling Compression Region (TCR) in the lobe and the underlying magnetic structure in the plasma sheet causing it. Previous work suggests that these structures are created by either single-X-line time-dependent reconnection, forming a flux-bulge, or multiple-X-line reconnection, forming a flux-rope. The observations are analysed and compared to the predictions of these models to determine which mode of reconnection created the structure. The second study presents an adaptation to a single particle model of time-dependent reconnection in the magnetotail previously published by Owen and Cowley (1987). This new model relaxes the cold plasma approximation and assesses the stress balance conditions on reconnected field lines threading the current sheet when the outflow particles have a perpendicular pressure. This is modeled as a result of pitch angle scattering of field-aligned inflow particles as they cross the current sheet on hairpin-like reconnected field lines. The new results show that this accounts for a flux-bulge and a TCR which is consistent with observations. The third study presents a numerical particle model which simulates the evolution of a plasmoid, modeled as a single magnetic field loop in the magnetotail. The model magnetotail has a magnetic, density and velocity gradient along the tail axis. The plasma within the plasmoid splits into two groups, the movement of these groups causes the plasmoid size to oscillate. The initial tailward movement of the plasmoid is caused by the magnetic gradient but continues in its absence due to the net momentum of the plasma inside the plasmoid, with the tailward travelling particles travel faster than the Earthward travelling particles.

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