Date of Award

8-2018

Document Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Engineering Physics

Department

Physical Sciences

Committee Chair

Dr. Matthew Zettergren

First Committee Member

Dr. Jonathan Snively

Second Committee Member

Dr. Kshitija Deshpande

Third Committee Member

Dr. Douglas Rowland

Abstract

Significant amounts of ionospheric plasma can be transported to high altitudes (ion upflow) in response to a variety of plasma heating and uplifting processes such as DC electric fields and precipitation. Once ions have been lifted to high altitudes, transverse ion acceleration by broadband ELF waves can give the upflowing ions sufficient energy for the mirror force to propel these ions to escape into the magnetosphere (ion outflow). In order to accurately examine the connection between upflow and outflow processes, a new two dimensional, anisotropic fluid model is developed.

The new model, named GEMINI-TIA, is based on a Bi-Maxwellian distribution function and solves the time-dependent, nonlinear equations of conservation of mass, momentum, parallel energy, and perpendicular energy for six ion species important to the E-, F-, and topside ionospheric regions: O+, NO+, N+ 2 , O+ 2 , N+, and H+. Electrons have also been included using an isotropic description. The effects of photoionization, electron impact ionization, wave particle interactions and chemical and collisional interactions with the neutral atmosphere are included. In order to facilitate comparisons with data, the model accepts as inputs the main drivers of ion upflow and outflow: particle precipitation, electric fields, ELF wave power, and neutral winds and densities. GEMINI-TIA is used here in parametric and realistic case studies of ion upflow and outflow.

In this research, GEMINI-TIA is first used in direct comparison with its parent isotropic model GEMINI to examine differences between isotropic and anisotropic descriptions of ionospheric upflow driven by DC electric fields. Further differences between isotropic and anisotropic descriptions of ionospheric upflow are examined through an additional comparison study that utilizes ionospheric drivers with realistic spatial and temporal variations. GEMINI-TIA, and its parent isotropic model GEMINI, are constrained by the MICA sounding rocket campaign data and respective outputs compared to analyze the impacts of anisotropy on low altitude ionospheric dynamics, specifically density cavity formation and related upflow.

Next, GEMINI-TIA is used in a parametric study to examine ionospheric upflow driven by DC electric fields, possible effects of low-altitude wave heating, and impacts of neutral winds on ion upflow. Simulations show significant responses at low altitudes to wave heating for very large power spectral densities, but ion temperature anisotropies below the F region peak are dominated by frictional heating from DC electric fields. The time history of the neutral winds is also shown to affect the amount of ions transported to higher altitudes by DC electric fields and BBELF waves.

Then, the role of neutral wind disturbances regulating ion outflow is further explored through model coupling between GEMINI-TIA and a neutral dynamics model guided by Sondrestrom ISR data. Specifically, a sequence of simulations with varying wave amplitude are conducted to determine responses to a range of transient forcing reminiscent of the ISR data. Thermospheric motions due to acoustic gravity waves (GWs) drive ion upflow in the F region, modulating the topside ionosphere in a way that can contribute to ion outflow.

Lastly, GEMINI-TIA is used to study the spatiotemporal limitations of data driven modeling using the ISINGLASS sounding rocket campaign. Realistic variability of energy inputs into the ionosphere, from both the thermosphere and magnetosphere, are important when accurately determining the ion upflow/outflow response. Ground data driven simulations capture the shape and duration of ion upflows/downflows more accurately by containing both time and space variability but at the loss of the fine scale details that are present in in situ measurements. During the ISINGLASS campaign, the auroral arc had a pronounced southward drift, not captured in the rocket measurements, which slowly moves energization regions across the ionosphere generating a finite amount of heating in any given location. The overall ionospheric response, including the locations and strengths of upflows and downflow, is highly dependent on the time history of the ionosphere.

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