Date of Award

Spring 2012

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Joachim Raeder

Abstract

Dispersed ion structures observed near the magnetosphere cusps have long been used to infer locations and properties of reconnection at the Earth's magnetopause. However, observations are often difficult to interpret since spacecraft move relative to a cusp ion structure, creating temporal/spatial ambiguity in the observations. Models of cusp ion structures are also limited to the cases during stable solar wind and IMF because empirical models are used to obtain the Earth's electromagnetic fields. In this dissertation, we develop a dynamic model of cusp ion structures usable for non-steady solar wind and IMF cases by using the Liouville Theorem Particle Tracer (LTPT) with the OpenGGCM 3D global MHD model. We first test our model's validity by reconstructing cusp ion structures observed from Cluster and Polar satellites. Our model faithfully reproduces various observed cusp ion structures, such as normal dispersion, reverse dispersion, double dispersions, and stepped dispersion. We also demonstrate our model's ability to investigate magnetopause processes that relate to the cusp structures. By analyzing the precipitating pattern of cusp ions and the magnetopause movement, we find that sudden increase of solar wind pressure, non-steady reconnection rates, and change of IMF clock angle cause the various dispersions in the Cluster and Polar observations. After the model validation test, we study the general relation between cusp ion structures and magnetopause processes during four different IMF clock angles of 0°, 60°, 120°, and 180°. Our model produces a reverse dispersion, double reverse dispersions, a flat and dispersed structure, and a normal dispersion under each IMF condition, respectively. From the detailed study of the ion entry points and the reconnection patterns on the magnetopause, we find that lobe reconnection, recurring FTE formation, coexistence of component and anti-parallel reconnection, and subsolar reconnection cause each cusp structure. We also find that cusp ions during northward IMF originate from an anti-parallel reconnection zone whose shear angle is over 170°. Conversely, during southward IMF ions precipitate not only from a high shear angle zone but also from a very low shear angle zone.

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