Date of Award
Doctor of Philosophy (PhD)
Astrophysical & Planetary Sciences
Robert E. Ergun
THEMIS is a recent multi-satellite mission launched in 2007 with five identical spacecraft orbiting in the equatorial plane of the Earth. Featuring a comprehensive package of particle and field instruments on each THEMIS spacecraft and multi-resolution data products, the THEMIS mission offers great opportunities to study space plasma dynamics in both large MHD scales and relatively small kinetic scales. This work focuses on kinetic aspects of space plasma dynamics using THEMIS observations, especially electric field observations, which are critical to study kinetic effects. Three specific topics, electron phase-space holes (EHs), kinetic instabilities in the lunar wake, and turbulent electric and magnetic fields in the Earth's magnetotail, are investigated in detail. EHs are good indicators of nonlinear activities in space plasmas and have attracted many interests in both observational and theoretical work. In a traditional theoretical picture, EHs are understood as purely electrostatic structures. However, THEMIS recently observed electromagnetic EHs, which cannot be fully described with traditional theory, in the plasma sheet boundary layer. This work seeks to understand the magnetic signals of the observed electromagnetic EHs. In addition to the interpretations of the observed magnetic signals, a statistical study of the properties of the observed electromagnetic EHs reveals that those electromagnetic EHs feature fast speeds, large sizes, and strong potentials, which intrigues interests in their generation mechanism and influences on the space plasma environment. The lunar wake, resulting from the interaction between the solar wind and the Moon, is an excellent example to study the expansion of plasmas into a more tenuous space. One of the THEMIS spacecraft, THB (known as ARTEMIS P1 after winter 2009) provided new observations of the lunar wake from a lunar-wake flyby in early 2010. Kinetic instabilities from that flyby are examined in this work. Wavelengths and phase velocities of the observed kinetic instabilities are derived from electric field instrument voltage measurements using interferometric techniques, providing unprecedented information of the properties of kinetic instabilities in the lunar wake. In addition, the mode of the observed kinetic instabilities is identified as the electron beam mode, confirming a global-scale dynamics, electron velocity filtration by the negative lunar-wake potential, as proposed in previous works. Turbulence, an efficient mechanism to dissipate kinetic energy into thermal energy, plays an important role in the global energy budget in the plasma sheet. Previous studies of turbulence in the plasma sheet generally focused on MHD scales and did not include electric field measurements. This work combines both electric and magnetic field measurements from THEMIS in the Earth's magnetotail with a frequency range that extends from MHD scales to kinetic scales. Statistical results of Poynting flux and spectral behavior of the turbulent electric and magnetic fields are presented. The Poynting flux results suggest that the turbulent electric and magnetic fields play an important role in the energy coupling between the ionosphere and the magnetosphere, whereas the spectral results may include information on universal relations between electric and magnetic fields for turbulence in plasmas.
Tao, Jianbao, "THEMIS Observations of Electron Phase-Space Holes, the Lunar Wake, and Turbulence" (2012). Astrophysical & Planetary Sciences Graduate Theses & Dissertations. 17.