Date of Award
Doctor of Philosophy in Applied Physics - (Ph.D.)
Jay R. Johnson
Dale E. Gary
The Earth magnetosphere contains energetic particles undergoing specific motions around Earth’s magnetic field, and interacting with a variety of waves. The dynamics of energetic particles are often described in terms of three kinds of adiabatic invariants. Energetic electrons are often unstable to the whistler-mode chorus waves, and ions, to the electromagnetic ion cyclotron (EMIC) instability. These waves play an important role in the dynamics of the magnetosphere by energizing electrons to form a radiation belt, extracting energy from the hot, anisotropic ions and causing pitch angle scattering of energetic ions and relativistic electrons into the loss cone. EMIC waves correspond to the highest frequency waves in the ultra-low frequency (ULF) spectral regime, and field line resonances at the lower frequency may serve as diagnostics for the plasma distribution in the magnetosphere. This dissertation investigates (1) a rapid, efficient way of specifying particle’s adiabatic motion in the magnetosphere, (2) source of the whistler-mode chorus waves, (3) physical properties and coherent spatial dimensions of the EMIC waves and (4) a diagnostic use of the toroidal mode Alfvén waves on the plasma density distribution in the Earth magnetosphere.
The studies presented in this dissertation have significantly been benefited from the comprehensive data obtained by several space missions, including the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft, Cluster mission, the Geostationary Operational Environment Satellites (GOES), Los Alamos National Laboratory (LANL) satellites, the Polar spacecraft and the Active Magnetospheric Particle Tracer Explorers (AMPTE)/Charge Composition Explorer (CCE), and from ground-based Automatic Geophysical Observatories (AGO).
The main findings and achievements in this dissertation are as follows: (1) A method of rapidly and efficiently computing the magnetic drift invariant (L*) was developed. This new method is not only fast enough for near real-time calculation of L*, enabling spacecraft tracking in this coordinates, but scalable to a large number of L* values that are often required for inter-comparison between simulation results and observations. (2) The relationship between the electron injection and the chorus waves was studied from the simultaneous observations of a substorm event on 23 March 2007 made in space and on ground. Timing analysis and a test particle simulation indicated that the electrons injected during the substorm could form a pitch-angle distribution suitable for the whistler-mode instability when they arrive near the dawn-side magnetopause. (3) The EMIC waves are found to occur ubiquitously throughout the outer magnetosphere and their properties distribute asymmetrically in local time. The asymmetry in the wave properties seems to be correlated with the electron density distribution and ion temperature anisotropy, as supported by a linear EMIC instability model. (4) The size of coherent activity of the EMIC waves was estimated using the multi-spacecraft observations made by the THEMIS spacecraft and cross correlation analysis. It is found that the characteristic dimension in the direction transverse to the local magnetic field is 2–3 times the local EMIC wavelength. (5) The global distribution of the equatorial mass density was derived from the toroidal mode standing Alfvén waves in an unprecedented spatial scale. The equatorial mass density is distributed asymmetrically with a bulge at the dusk sector and the magnitude falls logarithmically with increasing radial distance. It is confirmed that the variation in the derived mass density is only weakly related to the geomagnetic activity, but has strong correlation with the solar activity.
The major contribution of this dissertation is the extension of the scope of previous understanding of various plasma wave properties and energetic particle dynamics in the inner magnetosphere to outer magnetosphere by new, in-depth analyses of the data from the THEMIS, GOES and AMPTE/CCE missions.
Min, Kyungguk, "A statistical study of plasmawaves and energetic particles in the outer magnetosphere" (2013). Dissertations. 375.