Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
2 results
Search Results
Item The Effects of Turbulence on Magnetic Reconnection at the Magnetopause(2017) Price, Lora; Drake, James F; Swisdak, M M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Magnetic reconnection facilitates the conversion of magnetic energy to thermal energy and plasma flows. Reconnection occurs at the magnetopause, the magnetic boundary between the plasmas of the terrestrial magnetosphere and the heliosphere. Turbulence is known to develop at this boundary, but its influence on reconnection, particularly on small scales, is unknown. In light of this, an important goal of NASA's Magnetospheric Multiscale (MMS) Mission is to understand the role turbulence plays in the development of reconnection. We present two- and three-dimensional particle-in-cell simulations of the 16 October 2015 MMS magnetopause reconnection event. While the two-dimensional simulation is laminar, turbulence develops at both the x-line and along the magnetic separatrices in the three-dimensional simulation. This turbulence is electromagnetic, is characterized by a wavevector $k$ given by $k\rho_e\sim(m_e/m_i)^{0.25}$ with $\rho_e$ the electron Larmor radius, and appears to have the ion pressure gradient as its source of free energy. Taken together, these results suggest the instability is a variant of the lower-hybrid drift instability. The turbulence produces electric field fluctuations in the out-of-plane direction with an amplitude of around $\pm 10$ mV/m, which is much greater than the reconnection electric field of around $0.1$ mV/m. Such large values of the out-of-plane electric field have been identified in the MMS data. The turbulence in the simulation controls the scale lengths of the density profile and current layers, driving them closer to $\sqrt{\rho_e\rho_i}$ than the $\rho_e$ or $d_e$ scalings seen in 2D reconnection simulations, where $d_e$ is the electron inertial length. The turbulence produces both anomalous resistivity and anomalous viscosity. Each contribute significantly to breaking the frozen-in condition in the electron diffusion region. The crescent-shaped features in velocity space seen both in MMS observations and in two-dimensional simulations survive. We compare and contrast these results to a three-dimensional simulation of the 8 December 2015 MMS magnetopause reconnection event in which the reconnecting and out-of-plane guide fields are comparable. LHDI is still present in this event, although its appearance is modified by the presence of the guide field. The crescents also survive although, in agreement with MMS, their intensity decreases. Nevertheless, the developing turbulence remains strong.Item Neutral Gas and Plasma Interactions in the Polar Cusp(2012) Olson, David K.; Moore, Thomas E.; Coplan, Michael A.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)When the solar wind interacts with the Earth's magnetosphere, both energy and matter can be transferred across the magnetopause boundary. This transfer gives rise to numerous phenomena, including ion outflow and neutral upwelling in the polar cusps. These processes are caused by a transfer of energy to the ionospheric plasma and neutral gas through various mechanisms. The heated plasma or gas expands, increasing the density of the atmosphere at high altitudes by as much as a factor of two, and injecting ionospheric plasma into and even outside of the magnetosphere. These two phenomena are examined in two ways: A novel high energy (0.1--10 keV) spectrograph for ionospheric cusp ions was designed as part of the Rocket Experiment for Neutral Upwelling (RENU), a sounding rocket campaign carried out at the northern polar cusp to observe the electrodynamic properties of the cusp during a neutral upwelling event. This instrument is called the KeV Ion Magnetic Spectrograph (KIMS). Ion outflow in the ionosphere has shown evidence of correlation with both Poynting flux and soft electron precipitation in the cusp. The heat input from these energy sources might also affect neutral gas in the ionosphere, contributing to upwelling phenomena seen at the dayside cusp. Using data from the Fast Auroral Snapshot Explorer (FAST) and the Challenging Minisatellite Payload (CHAMP) satellites, correlations of electromagnetic and particle energy inputs are examined with both ion outflow and neutral upwelling in the cusp. The added ability to process large quantities of data quickly and reference the data between separate satellites in this statistical survey gives clues to the consistency of the observed correlations with ion outflow over time and to the relative importance of these energy sources in the neutral upwelling phenomenon. It also provides the ability to understand these connections in a broad spectrum of conditions of the Sun and solar wind as well as in the Earth's magnetosphere.