Date of Award
Dissertation - Open Access
Doctor of Philosophy in Engineering Physics
Dr. Matthew Zettergren
First Committee Member
Dr. Jonathan Snively
Second Committee Member
Dr. Kshitija Deshpande
Third Committee Member
Dr. Douglas Rowland
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.
Scholarly Commons Citation
Burleigh, Meghan R., "Impacts of Anisotropy, Wave Heating, and Neutral Winds on High-Latitude Ionospheric Dynamics" (2018). PhD Dissertations and Master's Theses. 408.