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Understanding the Formation of Magnetic Field And UNDERSTANDING THE FORMATION OF MAGNETIC FIELD AND PLASMA STRUCTURES IN THE MAGNETOTAIL VIA THE RECONNECTION PROCESS Segheen Beyene Mullard Space Science Laboratory Department of Space and Climate Physics University College London A thesis submitted to UCL for the degree of Doctor of Philosophy March 2013 1 I, Segheen Beyene, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Signed: The first study of the thesis has been previously published: Beyene, S., Owen, C. J., Walsh, A. P., Forsyth, C., Fazakerley, A. N., Kiehas, S., Dandouras, I., and Lucek, E.: Cluster observations of a transient signature in the magnetotail: implications for the mode of reconnection, Ann. Geophys., 29, 2131-2146, doi:10.5194/angeo-29-2131-2011, 2011 2 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 3 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. 4 Acknowledgements Firstly I would like to thank my supervisors, Professors Chris Owen and Andrew Fazakerley for their help and guidance over the years. Thank you to my parents for everything before and during the PhD, they went above and beyond their parental duty and I am very grateful of that. Thank you to my sister Melei for all of the help, knowledge and for looking out for me during the early years. Thank you to my brother, Aflay for the times he cooked dinner, for bringing me along to the Jay-Z and Kanye West concert and for being someone to hang out with during the breaks between work. Thank you to my sister Settit for the long talks about music and TV shows and the healthy eating and travelling you do that is inspiring. Thank you to my brother-in-law, Hermon, for helping me perfect the personal statement of my PhD application and for helping me with my car troubles. Thank you to Phillip Hunt for all the help during the undergrad days. Thank you to my office mates, Andrew Walsh, Colin Forsyth and Roger Duthie for answering my many questions. Thank you to all of the people who drove me to and from the lab: Kimberly Steed, Annie Wellbrock, Sheila Kanani, Missagh Medipour, Ehsan Pedram, Awat Rahimi & Paul Prior. Thank you to Dr. Stefan Kiehas, Dr. Elizabeth Lucek, Dr. Iannis Dandouras for helping on the first study and to the teams behind the Cluster Active Archive, the QSAS software and the CIS, PEACE and FGM instruments of Cluster. Finally, I would like to thank the Science and Technology Funding Council (STFC) for funding my PhD. 5 Contents Abstract ......................................................................................................... 3 Acknowledgements ....................................................................................... 5 Contents ......................................................................................................... 6 List of Figures ............................................................................................... 9 List of Tables ............................................................................................... 11 List of Acronyms ......................................................................................... 11 1 Introduction ........................................................................................... 12 1.1 Plasma Physics ............................................................................... 13 1.1.1 Plasma ...................................................................................... 13 1.1.2 Single particle motion .............................................................. 15 1.1.3 Kinetic Theory ......................................................................... 22 1.1.4 MagnetoHydroDynamics (MHD) ............................................ 23 1.2 Magnetospheric Physics ................................................................. 30 1.2.1 Coordinate systems .................................................................. 30 1.2.2 Solar Wind................................................................................ 31 1.2.3 Magnetosphere ......................................................................... 32 1.2.4 Dungey Cycle ........................................................................... 42 1.2.5 NENL model of Substorms ...................................................... 45 1.2.6 Travelling Compression Regions ............................................. 47 1.3 Modes of Reconnection .................................................................. 50 1.3.1 Multiple X-line Reconnection (MXR) ..................................... 50 1.3.2 MHD Model of Time Dependent Reconnection ...................... 54 1.3.3 Cold Particle Model of Time Dependent Reconnection .......... 60 2 Cluster Observations of a Transient Signature in the Magnetotail: Implications for the Mode of Reconnection ............................................... 62 2.1 Introduction .................................................................................... 62 2.2 Comparison of the Reconnection Products .................................... 64 6 2.3 Instrumentation ............................................................................... 65 2.3.1 FGM ......................................................................................... 66 2.3.2 PEACE ..................................................................................... 67 2.3.3 CIS ............................................................................................ 71 2.3.4 Cluster location and separation ................................................ 73 2.4 Observations ................................................................................... 74 2.5 Analysis .......................................................................................... 89 2.5.1 Orientation of Magnetic Structure ........................................... 89 2.5.2 Velocity Calculation ................................................................. 90 2.5.3 Configuration in MVA derived co-ordinate system ................ 93 2.5.4 Observations in MVA derived co-ordinate system .................. 95 2.6 Discussion ....................................................................................... 99 2.6.1 Interpretation of observations .................................................. 99 2.6.2 Multiple-X-line Reconnection Interpretation ........................ 104 2.6.3 Time Dependent Reconnection Interpretation ....................... 105 2.7 Conclusions .................................................................................. 106 Chapter 3 ................................................................................................... 108 3 Modelling the Effects of Time-Varying Reconnection Leading to the Formation of Travelling Compression Regions in the Magnetotail ......... 108 3.1 Introduction .................................................................................. 108 3.1.1 Comparison of the two existing models ................................. 109 3.2 Cold Particle Model of Time-Dependent Reconnection .............. 110 3.2.1 Marginal Firehose Stability Equation .................................... 110 3.2.2 Frames of Reference .............................................................. 113 3.2.3 Separatrix Height ................................................................... 116 3.2.4 Height of PO boundary .......................................................... 120 3.3 A New Hot Particle Model of Time-Dependent Reconnection ... 124 3.3.1 Horizontal Stress balance ....................................................... 124 3.3.2
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