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Title: The dynamics of the outer boundaries in global simulations of planetary magnetospheres
Author: Mejnertsen, Lars
ISNI:       0000 0004 7658 4516
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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The solar wind-magnetosphere interaction consists of a set of coupled regions with different dominating physical processes. Understanding this interaction is important in both furthering our understanding of space plasma physics, and mitigating the effects of space weather. The outer boundaries of the magnetosphere are important as they mediate variations in the solar wind and their impact on magnetospheric dynamics. The Gorgon magnetohydrodynamic code is developed to simulate planetary magnetospheres. It is benchmarked in the context of the Earth's magnetosphere, where it performs well compared to other global MHD codes. The code is used to study the behaviour of the outer boundaries of the magnetosphere, the bow shock and magnetopause, focussing on their response to different magnetospheric drivers. Gorgon is first adapted to Neptune's magnetosphere, whose dipole is significantly tilted from its rotation axis. The outer boundaries undergo daily variation, resulting in reconnection being heavily modulated by the precessing internal field. The results found have implications on the global circulation of plasma and energy in inclined magnetospheres, emphasising the need for three-dimensional, time-dependent simulations. The Earth's magnetosphere is studied using real varying solar wind, where the outer boundaries' position and velocity undergo rapid changes. The variable solar wind and curved bow shock causes different parts of the bow shock to respond differently which not captured in empirical models that are widely used to place spacecraft observations in context. In situ observations of the shock may be biased toward observing high velocity shocks, as they rarely cross a stationary shock. A complex mesh of flux ropes are also formed. Their generation creates complex topology, which affects their subsequent evolution, allowing some flux ropes far into the tail. Their complex topology has interesting consequences on the impact these flux ropes have on the transfer of magnetic flux and plasma into magnetosphere.
Supervisor: Eastwood, Jonathan ; Chittenden, Jeremy Sponsor: Science and Technology Facilities Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral