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Magnetosphere-Ionosphere Coupling During Substorms Open Access


Other title
magnetosphere-ionosphere coupling
Type of item
Degree grantor
University of Alberta
Author or creator
Murphy, Kyle R
Supervisor and department
Mann, Ian (Physics)
Examining committee member and department
Lysak, Bob (University of Minnesota, Physics)
Moore, Roger (Physics)
Fenrich, Francis (Physics)
Sydora, Richard (Physics)
Department of Physics

Date accepted
Graduation date
Doctor of Philosophy
Degree level
This thesis concerns the development and evolution of the magnetospheric substorm. In particular this thesis concentrates on the dynamics of Ultra Low Frequency (ULF) waves during the substorm growth and expansion phases, the coupling of the ionosphere and magnetosphere through substorm onset and the substorm expansion phase and the location in the magnetosphere and physical processes leading to substorm onset. Firstly we present a superposed epoch analysis of ULF waves through the substorm growth and expansion phase, characterizing the two dimensional distribution of power spectral density and polarization of these waves with respect to auroral onset. We demonstrate that ULF wave power during substorms is characteristic of a power law and that the distribution of wave power and polarization is consistent with the expected pattern in the presence of a substorm current wedge. Secondly we examine the global field aligned current (FAC) morphology through the substorm growth and expansion phase. We demonstrate, for the first time, that there is a clear reduction in FACs coupling the ionosphere and magnetosphere just prior to substorm onset. We suggest that this change in coupling may play an important role in the destabilization of the magnetosphere at substorm onset. We also present the first two‐dimensional in‐situ observation of the FACs and ionospheric current sheets comprising the substorm current wedge in the substorm expansion phase. We demonstrate that the structure of the substorm current wedge is significantly more complex than the classical view of the substorm current wedge. Finally we present a comprehensive ground and in‐situ analysis of two substorms to determine where in the magnetosphere the substorms initiate. We demonstrate that both substorms initiate on closed field lines in the inner magnetosphere. More significantly we demonstrate that magnetic reconnection can follow substorm onset and that earthward magnetotail flows or auroral streamers, their ionospheric counterparts, are not a necessary condition for substorm onset.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Murphy, K. R., I. J. Rae, I. R. Mann, and D. K. Milling (2011), On the nature of ULF wave power during nightside auroral activations and substorms: 1. Spatial distribution, J. Geophys. Res., 116, A00I21, doi:10.1029/2010JA015757.Murphy, K. R., I. R. Mann, I. J. Rae, C. L. Waters, B. J. Anderson, D. K. Milling, H. J. Singer, and H. Korth (2012), Reduction in field-aligned currents preceding and local to auroral substorm onset, Geophys. Res. Lett., 39, L15106, doi:10.1029/2012GL052798.Murphy, K. R., I. R. Mann, I. J. Rae, C. L. Waters, H. U. Frey, A. Kale, H. J. Singer, B. J. Anderson, and H. Korth (2013), The detailed spatial structure of field-aligned currents comprising the substorm current wedge, J. Geophys. Res. Space Physics, 118, doi:10.1002/2013JA018979.

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