Date of Award
Thesis - Open Access
Master of Science in Engineering Physics
Dr. Matthew Zettergren
First Committee Member
Dr. John Hughes
Second Committee Member
Dr. Jonathan Snively
Large upwellings of thermal plasma are commonly observed in the high-latitude, topside ionosphere. These auroral ion upflows have a range of potential sources including frictional heating, electron precipitation, neutral winds, and higher-altitude density cavities. The unique signatures and detailed evolution of these upflows are examined through the use of Incoherent Scatter Radar data and a sophisticated ionospheric fluid model.
A survey of solar cycle 23 shows that at Sondrestrom upflows occur most often in the cusp region and midnight auroral zone. Simplified force balance analysis and steady state velocity calculations are applied to a few select events to elucidate the role of the neutral wind in ion upflows. In some cases, the data suggests that neutral winds are necessary to balance the forces at lower altitudes. Detailed modeling shows that neutral winds will directly impact the efficiency of ion upflow mechanisms, and can create factors of ∼ 2-4 enhancements in upward ion fluxes in the topside ionosphere. Through detailed modeling, it has been shown that the commonly used steady state momentum equations are not consistently valid above ∼ 450 km. The significant transient effects, that exist at the high altitudes, imply that instantaneous input/output relationships for parameterizing ion outflow are likely inadequate. Steady state velocity calculations, in both radar data and simulations, tend to grossly over/underestimate speeds when the ions are accelerating/decelerating at high altitudes.
A systematic simulation study of the efficiency and transient responses of the ionospheric upflow to various energy sources is also conducted. For this study, applied electric potentials were varied from 50 to 150 mV/m in 10 mV/m increments, electron precipitation effects peaking at a range from 2 to 20 mW/m 2 were varied in 2 mW/m2 increments, and density cavities were varied from 10% depletion up to 80% depletion in 10% increments. These results generally reveal that the propagation time delay between the F-region where the upflows are initiated and higher-altitudes is highly amplitude dependent. Electric fields exceeding 110 mV/m or particle fluxes exceeding 18 mW/m 2 create tremendous fluxes (10 13 m-3 s-1 ) of plasma that likely act as source populations for other energization processes above the ionosphere. Above 750 km, high altitude responses are not purely wave-like and include the dissipative effects of heat fluxes and heat exchange along with other complexities such as O + -H resonant charge exchange.
Scholarly Commons Citation
Burleigh, Meghan R., "Auroral Ion Upflows: Sources, High Altitude Dynamics, and Neutral Wind Effects" (2013). PhD Dissertations and Master's Theses. 33.