Transport and energization of heavy ions in earth’s high latitude ionosphere

Lin, Mei-Yun

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https://hdl.handle.net/2142/121964 Copy

Description

Title

Transport and energization of heavy ions in earth’s high latitude ionosphere

Author(s)

Lin, Mei-Yun

Issue Date

2023-10-30

Director of Research (if dissertation) or Advisor (if thesis)

Ilie, Raluca

Doctoral Committee Chair(s)

Ilie, Raluca

Committee Member(s)

• Kudeki, Erhan
• Bernhard, Jennifer
• Makela, Jonathan
• Glocer, Alex

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Ion Outflow
• Atmospheric Escape
• Polar Wind
• Heavy Ion
• Molecular Ion

Abstract

Changes in the plasma composition in the terrestrial environment regulate the interactions between the Earth's electromagnetic environment and the solar wind. Ions with larger masses but low-charge states play a crucial role in controlling the mass and energy flow from the low-altitude atmosphere and significantly impact the dynamics and morphology of near-Earth current systems. The presence of heavy ions alters the mass loading of the plasma, affects wave generation and propagation, and impacts the formation and transport of other energetic ion populations. Identifying the processes responsible for particle energization is one of the open questions in Heliophysics research, whether it pertains to coronal heating, polar wind outflow, or magnetospheric transport. Furthermore, it holds the key to understanding the response of the Earth’s terrestrial environment to solar wind driving. Atomic N+ and O+, as well as molecular N2+, NO+ and O2+ ions, are the major species in the Earth's low-altitude atmosphere. While numerous studies have focused on the dynamics of the ionospheric O+ ions, the relative contribution of outflowing N+ and molecular ion species to the ionospheric outflow is not understood at this time due to the limiting capabilities of instruments flying in space to distinguish between the two species. Albeit limited, the existing observational records suggest that outflowing N+ are constant companions of O+ ions at all times. Moreover, during geomagnetically active times, the presence of outflowing molecular ions was often accompanied by a high ratio of N+/O+ in the near-Earth plasma. However, the transport and energization of N+ and molecular ions from a few hundred to hundreds of thousands of kilometers have yet to be discovered, and limited knowledge of their circulations in the terrestrial environment is currently available. This thesis presents the first physics-based numerical model, the Seven ions Polar Wind Outflow Model (7iPWOM), that solves and tracks the evolution of all relevant ion species (H+, He+, N+, O+, N2+, NO+, and O2+) in the ionosphere. Numerical simulations based on this newly developed model provided insight into what controls the global and local dynamical changes in the ionospheric plasma composition and determined the energization mechanisms responsible for their vertical transport from the high latitude atmosphere to the near-Earth space. The 7iPWOM solves the gyrotropic transport equations from two hundred to a thousand kilometers in the ionosphere and transitions to a kinetic approach in the high-altitude regions. To account for and describe the dynamics of N+ N2+, NO+, and O2+ ions in the high latitude ionosphere, advanced schemes for production and energization mechanisms, including ion-electron-neutral chemistry and collisions, suprathermal electron impact, and resonance wave heating, have been developed and implemented in the model. Moreover, a global solution of the ionospheric outflow was obtained by modeling the transport and energization of this cold plasma, both across the polar cap and from low to high altitudes along magnetic flux tubes involving thousands of magnetic field lines. To assess the contribution of N+ to the ionospheric outflow, a series of numerical simulations was designed to probe the influence of season, solar activity, and various geomagnetic activity conditions. These simulations demonstrated the critical role N+ ions play in the ionospheric outflow for all conditions: independent of illumination, season, and solar conditions, the presence of N+ ions in the polar wind significantly alters the solution of all other species while providing an excellent prediction of the polar wind solution as compared with observations. Furthermore, the results of a parameter study using the kinetic version of 7iPWOM have revealed place bounds on the efficacy of resonant wave-particle interaction. These numerical experiments suggest that heavier ion species are highly sensitive to the wave spectrum and display the so-called “valve” effect: a minimum threshold in wave energy is needed to loft the molecular ions against the Earth's gravitational potential. Due to the limited supply of molecular ions from the ionosphere, their abundance and fluxes are regulated by the timescale of production and loss at lower altitudes as well as the composition of the ionospheric plasma, while the wave energy mainly controls how far up molecular ions are transported. Finally, this thesis is complemented by a series of studies that contribute to promoting Diversity, Equity, and Inclusion within the Space Science community. The preceding research endeavors encompass an exploration of the challenges faced by underrepresented gender groups in STEM fields and a comprehensive review of potential remedies. Furthermore, a survey was conducted within an engineering department at a U.S. university, and a pilot study was implemented to evaluate the impact of a DEI initiative on the motivation of gender-minority students to pursue research careers.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Mei-Yun Lin

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